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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Feb. 15, 2019	Jun. 29, 2018
Document and Entity Information
Entity Registrant Name	COMFORT SYSTEMS USA INC
Entity Central Index Key	0001035983
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		36,869,712
Entity Public Float			$ 1,670

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
CURRENT ASSETS:
Cash and cash equivalents	$ 45,620	$ 36,542
Billed accounts receivable, less allowance for doubtful accounts of $5,898 and $3,400, respectively	481,366	382,867
Unbilled accounts receivable	37,180
Other receivables	16,361	21,235
Inventories	12,416	10,303
Prepaid expenses and other	6,544	8,294
Costs and estimated earnings in excess of billings	10,213	30,116
Total current assets	609,700	489,357
PROPERTY AND EQUIPMENT, NET	99,618	87,591
GOODWILL	235,182	200,584
IDENTIFIABLE INTANGIBLE ASSETS, NET	95,275	76,044
DEFERRED TAX ASSETS	17,634	22,966
OTHER NONCURRENT ASSETS	5,155	4,578
Total assets	1,062,564	881,120
CURRENT LIABILITIES:
Current maturities of long-term debt	3,279	613
Accounts payable	176,167	132,011
Accrued compensation and benefits	87,388	69,217
Billings in excess of costs and estimated earnings	130,986	106,005
Accrued self-insurance	36,386	32,228
Other current liabilities	32,852	33,654
Total current liabilities	467,058	373,728
LONG-TERM DEBT	73,639	59,926
DEFERRED TAX LIABILITIES	1,387	2,263
OTHER LONG-TERM LIABILITIES	22,433	27,258
Total liabilities	564,517	463,175
COMMITMENTS AND CONTINGENCIES
STOCKHOLDERS' EQUITY:
Preferred stock, $.01 par, 5,000,000 shares authorized, none issued and outstanding
Common stock, $.01 par, 102,969,912 shares authorized, 41,123,365 and 41,123,365 shares issued, respectively	411	411
Treasury stock, at cost, 4,229,653 and 3,936,291 shares, respectively	(87,747)	(63,519)
Additional paid-in capital	316,479	312,784
Retained earnings	268,904	168,269
Total stockholders’ equity	498,047	417,945
Total liabilities and stockholders’ equity	$ 1,062,564	$ 881,120

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED BALANCE SHEETS
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 5,898	$ 3,400
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	102,969,912	102,969,912
Common stock, shares issued	41,123,365	41,123,365
Treasury stock, shares	4,229,653	3,936,291

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CONSOLIDATED STATEMENTS OF OPERATIONS
REVENUE	$ 2,182,879	$ 1,787,922	$ 1,634,340
COST OF SERVICES	1,736,600	1,421,641	1,290,331
Gross profit	446,279	366,281	344,009
SELLING, GENERAL AND ADMINISTRATIVE EXPENSES	296,986	266,586	243,201
GOODWILL IMPAIRMENT		1,105
GAIN ON SALE OF ASSETS	(945)	(670)	(761)
Operating income	150,238	99,260	101,569
OTHER INCOME (EXPENSE):
Interest income	73	70	9
Interest expense	(3,710)	(3,156)	(2,345)
Changes in the fair value of contingent earn-out obligations	(2,066)	3,715	731
Other	4,141	1,049	1,097
Other income (expense)	(1,562)	1,678	(508)
INCOME BEFORE INCOME TAXES	148,676	100,938	101,061
PROVISION FOR INCOME TAXES	35,773	45,666	36,165
NET INCOME	$ 112,903	$ 55,272	$ 64,896
INCOME PER SHARE:
Basic (in shares)	$ 3.03	$ 1.48	$ 1.74
Diluted (in shares)	$ 3.00	$ 1.47	$ 1.72
SHARES USED IN COMPUTING INCOME PER SHARE:
Basic (in shares)	37,202	37,239	37,335
Diluted (in shares)	37,592	37,672	37,811
DIVIDENDS PER SHARE (in dollars per share)	$ 0.330	$ 0.295	$ 0.275

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Non-Controlling Interests	Total
BALANCE at Dec. 31, 2015	$ 411	$ (46,845)	$ 323,765	$ 69,390	$ 18,284	$ 365,005
BALANCE (in shares) at Dec. 31, 2015	41,123,365
BALANCE (in shares) at Dec. 31, 2015		(3,696,781)
Increase (Decrease) in Stockholders' Equity
Net income				64,896		64,896
Issuance of Stock:
Issuance of shares for options exercised		$ 1,568	10			1,578
Issuance of shares for options exercised (in shares)		111,761
Issuance of restricted stock & performance stock		$ 2,282	(306)			1,976
Issuance of restricted stock & performance stock (in shares)		172,727
Shares received in lieu of tax withholding payment on vested restricted stock		$ (1,304)				(1,304)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(41,788)
Stock-based compensation			3,502			3,502
Dividends				(10,264)		(10,264)
Acquisition of noncontrolling interests			(17,346)		$ (18,284)	(35,630)
Share repurchase		$ (13,088)				(13,088)
Share repurchase (in shares)		(460,170)
BALANCE at Dec. 31, 2016	$ 411	$ (57,387)	309,625	123,984		376,633
BALANCE (in shares) at Dec. 31, 2016	41,123,365
BALANCE (in shares) at Dec. 31, 2016		(3,914,251)
Cumulative effect of change in accounting principle at Dec. 31, 2016				(38)		(38)
Increase (Decrease) in Stockholders' Equity
Net income				55,272		55,272
Issuance of Stock:
Issuance of shares for options exercised		$ 2,257	(205)			2,052
Issuance of shares for options exercised (in shares)		(145,746)
Issuance of restricted stock & performance stock		$ 2,037	(421)			1,616
Issuance of restricted stock & performance stock (in shares)		(134,646)
Shares received in lieu of tax withholding payment on vested restricted stock		$ (1,419)				(1,419)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(39,335)
Stock-based compensation			3,785			3,785
Dividends				(10,987)		(10,987)
Share repurchase		$ (9,007)				(9,007)
Share repurchase (in shares)		(263,097)
BALANCE at Dec. 31, 2017	$ 411	$ (63,519)	312,784	168,269		$ 417,945
BALANCE (in shares) at Dec. 31, 2017	41,123,365					41,123,365
BALANCE (in shares) at Dec. 31, 2017		(3,936,291)				3,936,291
Increase (Decrease) in Stockholders' Equity
Net income				112,903		$ 112,903
Issuance of Stock:
Issuance of shares for options exercised		$ 3,618	(513)			3,105
Issuance of shares for options exercised (in shares)		(206,875)
Issuance of restricted stock & performance stock		$ 2,227	(4)			2,223
Issuance of restricted stock & performance stock (in shares)		(129,569)
Shares received in lieu of tax withholding payment on vested restricted stock		$ (1,540)				(1,540)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(36,967)
Stock-based compensation			4,212			4,212
Dividends				(12,268)		(12,268)
Share repurchase		$ (28,533)				(28,533)
Share repurchase (in shares)		(592,839)
BALANCE at Dec. 31, 2018	$ 411	$ (87,747)	$ 316,479	$ 268,904		$ 498,047
BALANCE (in shares) at Dec. 31, 2018	41,123,365					41,123,365
BALANCE (in shares) at Dec. 31, 2018		(4,229,653)				4,229,653

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 112,903	$ 55,272	$ 64,896
Adjustments to reconcile net income to net cash provided by operating activities—
Amortization of identifiable intangible assets	20,089	17,404	8,185
Depreciation expense	22,600	20,052	17,981
Goodwill impairment		1,105
Bad debt expense (benefit)	3,562	182	(27)
Deferred tax provision (benefit)	4,456	4,178	(1,239)
Amortization of debt financing costs	383	376	367
Gain on sale of assets	(945)	(670)	(761)
Changes in the fair value of contingent earn-out obligations	2,066	(3,715)	(731)
Stock-based compensation	7,161	6,377	5,041
(Increase) decrease in—
Receivables, net	(68,621)	(37,799)	7,038
Inventories	(1,538)	(584)	213
Prepaid expenses and other current assets	519	2,467	(8,850)
Costs and estimated earnings in excess of billings and unbilled accounts receivable	(14,444)	1,869	3,144
Other noncurrent assets	(114)	1,005	(143)
Increase (decrease) in—
Accounts payable and accrued liabilities	47,871	22,068	2,736
Billings in excess of costs and estimated earnings	16,786	13,265	(8,351)
Other long-term liabilities	(5,544)	11,238	1,689
Net cash provided by operating activities	147,190	114,090	91,188
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(27,268)	(35,467)	(23,217)
Proceeds from sales of property and equipment	1,698	1,359	1,062
Cash paid for acquisitions, net of cash acquired	(70,140)	(94,860)	(57,163)
Net cash used in investing activities	(95,710)	(128,968)	(79,318)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit	124,000	177,000	144,000
Payments on revolving line of credit	(119,000)	(132,000)	(154,000)
Payments on other debt	(1,127)	(835)	(592)
Payments on capital lease obligations		(256)	(251)
Debt financing costs	(844)		(789)
Payments of dividends to stockholders	(12,268)	(10,987)	(10,264)
Share repurchase	(28,533)	(9,007)	(13,088)
Shares received in lieu of tax withholding	(1,540)	(1,419)	(1,304)
Proceeds from exercise of options	3,105	2,052	1,578
Deferred acquisition payments	(750)	(2,802)	(1,350)
Payments for contingent consideration arrangements	(5,445)	(2,400)	(200)
Net cash provided by (used in) financing activities	(42,402)	19,346	(36,260)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	9,078	4,468	(24,390)
CASH AND CASH EQUIVALENTS, beginning of year	36,542	32,074	56,464
CASH AND CASH EQUIVALENTS, end of year	$ 45,620	$ 36,542	$ 32,074

Business and Organization	12 Months Ended
Business and Organization	Dec. 31, 2018
Business and Organization
Business and Organization	1. Business and Organization Comfort Systems USA, Inc., a Delaware corporation, provides comprehensive mechanical contracting services, which principally includes heating, ventilation and air conditioning (“HVAC”), plumbing, piping and controls, as well as off-site construction, electrical, monitoring and fire protection. We install, maintain, repair and replace products and systems throughout the United States. Approximately 38.0% of our consolidated 2018 revenue is attributable to installation of systems in newly constructed facilities, with the remaining 62.0% attributable to maintenance, repair and replacement services. The terms “Comfort Systems,” “we,” “us,” or “the Company,” refer to Comfort Systems USA, Inc. or Comfort Systems USA, Inc. and its consolidated subsidiaries, as appropriate in the context.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Principles of Consolidation

These financial statements are prepared in accordance with accounting principles generally accepted in the United States of America. The accompanying consolidated financial statements include our accounts and those of our subsidiaries in which we have a controlling interest. All significant intercompany accounts and transactions have been eliminated. Certain amounts in prior periods may have been reclassified to conform to the current period presentation. The effects of the reclassifications were not material to the consolidated financial statements.

Use of Estimates

The preparation of financial statements in conformity with generally accepted accounting principles requires the use of estimates and assumptions by management in determining the reported amounts of assets and liabilities, revenue and expenses and disclosures regarding contingent assets and liabilities. Actual results could differ from those estimates. The most significant estimates used in our financial statements affect revenue and cost recognition for construction contracts, the allowance for doubtful accounts, self‑insurance accruals, deferred tax assets, warranty accruals, fair value accounting for acquisitions and the quantification of fair value for reporting units in connection with our goodwill impairment testing.

Cash Flow Information

We consider all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.

Cash paid (in thousands) for:


	Year Ended December 31,
	2018		2017		2016
Interest	$	3,743	$	2,832	$	1,864
Income taxes	$	33,401	$	38,144	$	29,349

Recent Accounting Pronouncements

In May 2014, the FASB issued Accounting Standards Update (“ASU”) No. 2014-09, “Revenue from Contracts with Customers (Topic 606).” Topic 606 supersedes the revenue recognition requirements in “Revenue Recognition (Topic 605)” and requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. We adopted Topic 606 as of January 1, 2018.

In accordance with Topic 606, we applied the modified retrospective method to those contracts which were not completed as of January 1, 2018. Under the modified retrospective method, the cumulative effect of applying the standard is recognized at the date of initial application. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with our historic accounting under Topic 605.

In implementing Topic 606, we were required to recalculate the revenue earned on any work in process at the implementation date and to restate the revenue and cost of services as if Topic 606 had been followed from the inception of the contract. In recalculating costs and revenue under Topic 606 guidelines, we identified no material difference in the account balances. Since a material difference was not found, no retrospective analysis of account balance changes was required.

In August 2016, the FASB issued ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments”. This standard provides guidance on how certain cash receipts and cash payments are presented and classified in the statement of cash flows and is intended to reduce diversity in practice with respect to these items. The standard is applied using a retrospective transition method and is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We adopted this standard on January 1, 2018 and the adoption did not have any impact on our consolidated financial statements.

In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)”. The standard requires substantially all leases (with the exception of leases with a term of one year or less) to be recorded on the balance sheet using a method referred to as the right-of-use asset approach. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018 and interim periods within those years. Early adoption is permitted. Full retrospective application is prohibited. We plan to use a transition method allowed by ASU No. 2018-11, “Leases (Topic 842) Targeted Improvements” in which lessees apply the new lease standard on the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We do not expect the adoption of ASU 2016-02 to have a significant impact to our Statement of Operations or Cash Flows. Our Balance Sheet will be impacted from this standard by recording right-of-use assets and lease liabilities, which we currently expect to be less than $75 million.

In August 2018, the FASB issued ASU No. 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement”. This standard removes certain disclosure requirements including the valuation processes for Level 3 fair value measurements, the policy for timing of transfers between levels and the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy. The standard requires certain additional disclosures for public entities, including disclosure of the changes in unrealized gains and losses included in Other Comprehensive Income for Level 3 fair value measurements and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019 and interim periods within those years. Certain amendments, including the amendment on changes in unrealized gains and losses and the range and weighted average of significant unobservable inputs, should be applied prospectively while other amendments should be applied retrospectively to all periods presented upon their effective date. We are currently evaluating the potential impact of this authoritative guidance on our consolidated financial statements.

Revenue Recognition

Revenue is recognized when control of the promised goods or services is transferred to our customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods or services. Sales-based taxes are excluded from revenue.

We provide comprehensive mechanical contracting services, which principally includes HVAC, plumbing, piping and controls, as well as off‑site construction, electrical, monitoring and fire protection. We install, maintain, repair and replace products and systems throughout the United States. All of our revenue is recognized over time as we deliver goods and services to our customers. Revenue can be earned based on an agreed upon fixed price or based on actual costs incurred, marked up at an agreed upon percentage.

For fixed price agreements, we use the percentage of completion method of accounting under which contract revenue recognizable at any time during the life of a contract is determined by multiplying expected total contract revenue by the percentage of contract costs incurred at any time to total estimated contract costs. More specifically, as part of the negotiation and bidding process to obtain installation contracts, we estimate our contract costs, which include all direct materials, labor and subcontract costs and indirect costs related to contract performance, such as indirect labor, supplies, tools, repairs and depreciation costs. These contract costs are included in our results of operations under the caption “Cost of Services.” Then, as we perform under those contracts, we measure costs incurred, compare them to total estimated costs to complete the contract and recognize a corresponding proportion of contract revenue. Labor costs are considered to be incurred as the work is performed. Subcontractor labor is recognized as the work is performed. Non‑labor project costs consist of purchased equipment, prefabricated materials and other materials. Purchased equipment on our projects is substantially produced to job specifications and is a value-added element to our work. The costs are considered to be incurred when title is transferred to us, which typically is upon delivery to the work site. Prefabricated materials, such as ductwork and piping, are generally performed at our shops and recognized as contract costs when fabricated for the unique specifications of the job. Other materials costs are generally recorded when delivered to the work site. This measurement and comparison process requires updates to the estimate of total costs to complete the contract, and these updates may include subjective assessments and judgments.

We account for a contract when: (i) it has approval and commitment from both parties, (ii) the rights of the parties are identified, (iii) payment terms are identified, (iv) the contract has commercial substance, and (v) collectability of consideration is probable. We consider the start of a project to be when the above criteria have been met and we either have written authorization from the customer to proceed or an executed contract.

Selling, marketing and estimation costs incurred in relation to selling contracts are expensed as incurred. On rare occasions, we may incur significant expenses related to selling a contract that we only incurred because we sold that contract. If this occurs, we capitalize that cost and amortize it on a percentage of completion basis over the life of the contract. We do not currently have any capitalized selling, marketing, or estimation costs on our Balance Sheet and did not incur any impairment loss in the current year.

We generally do not incur significant incremental costs related to obtaining or fulfilling a contract prior to the start of a project. On rare occasions, when significant pre‑contract costs are incurred, they are capitalized and amortized on a percentage of completion basis over the life of the contract. We do not currently have any capitalized obtaining or fulfillment costs on our Balance Sheet and did not incur any impairment loss on such costs in the current year.

Project contracts typically provide for a schedule of billings or invoices to the customer based on our job to date percentage of completion of specific tasks inherent in the fulfillment of our performance obligation(s). The schedules for such billings usually do not precisely match the schedule on which costs are incurred. As a result, contract revenue recognized in the statement of operations can and usually does differ from amounts that can be billed or invoiced to the customer at any point during the contract. Amounts by which cumulative contract revenue recognized on a contract as of a given date exceed cumulative billings and unbilled receivables to the customer under the contract are reflected as a current asset in our balance sheet under the caption “Costs and estimated earnings in excess of billings.” Amounts by which cumulative billings to the customer under a contract as of a given date exceed cumulative contract revenue recognized on the contract are reflected as a current liability in our balance sheet under the caption “Billings in excess of costs and estimated earnings.”

Contracts in progress are as follows (in thousands):


	December 31,
	2018		2017
Costs incurred on contracts in progress	$	1,574,460	$	1,288,330
Estimated earnings, net of losses		300,514		253,641
Less—Billings to date		(1,958,567)		(1,617,860)
Less—Unbilled accounts receivable		(37,180)		—
	$	(120,773)	$	(75,889)

Costs and estimated earnings in excess of billings	$	10,213	$	30,116
Billings in excess of costs and estimated earnings		(130,986)		(106,005)
	$	(120,773)	$	(75,889)

Accounts receivable include amounts billed to customers under retention or retainage provisions in construction contracts. Such provisions are standard in our industry and usually allow for a small portion of progress billings or the contract price to be withheld by the customer until after we have completed work on the project, typically for a period of six months. Based on our experience with similar contracts in recent years, the majority of our billings for such retention balances at each balance sheet date are finalized and collected within the subsequent year. Retention balances at December 31, 2018 and 2017 were $80.8 million and $68.7 million, respectively, and are included in accounts receivable.

Accounts payable at December 31, 2018 and 2017 included $13.7 million and $11.9 million of retainage under terms of contracts with subcontractors, respectively. The majority of the retention balances at each balance sheet date are finalized and paid within the subsequent year.

The percentage of completion method of accounting is also affected by changes in job performance, job conditions, and final contract settlements. These factors may result in revisions to estimated costs and, therefore, revenue. Such revisions are frequently based on further estimates and subjective assessments. The effects of these revisions are recognized in the period in which revisions are determined. When such revisions lead to a conclusion that a loss will be recognized on a contract, the full amount of the estimated ultimate loss is recognized in the period such conclusion is reached, regardless of the percentage of completion of the contract.

Revisions to project costs and conditions can give rise to change orders under which the customer agrees to pay additional contract price. Revisions can also result in claims we might make against the customer to recover project variances that have not been satisfactorily addressed through change orders with the customer. Except in certain circumstances, we do not recognize revenue or margin based on change orders or claims until they have been agreed upon with the customer. The amount of revenue associated with unapproved change orders and claims was immaterial for the year ended December 31, 2018.

Variations from estimated project costs could have a significant impact on our operating results, depending on project size, and the recoverability of the variation via additional customer payments.

We typically invoice our customers with payment terms of net due in 30 days. It is common in the construction industry for a contract to specify more lenient payment terms allowing the customer 45 to 60 days to make their payment. It is also common for the contract in the construction industry to specify that a general contractor is not required to submit payments to a subcontractor until it has received those funds from the owner or funding source. In most instances we receive payment of our invoices between 30 to 90 days of the date of the invoice.

A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account in ASC Topic 606. A contract’s transaction price is allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied.

To determine the proper revenue recognition method for contracts, we evaluate whether two or more contracts should be combined and accounted for as one performance obligation and whether the combined or single contract should be accounted for as more than one performance obligation. This evaluation requires significant judgment and the decision to combine a group of contracts or separate the combined or single contract into multiple performance obligations could change the amount of revenue and profit recorded in a given period. For most of our contracts, the customer contracts with us to provide a significant service of integrating a complex set of tasks and components into a single project or capability (even if that single project results in the delivery of multiple units). Hence, the entire contract is accounted for as one performance obligation. Less commonly, however, we may promise to provide distinct goods or services within a contract, in which case we separate the contract into more than one performance obligation. If a contract is separated into more than one performance obligation, we allocate the total transaction price to each performance obligation in an amount based on the estimated relative standalone selling prices of the promised goods or services underlying each performance obligation. We infrequently sell standard products with observable standalone sales. In cases where we do, the observable standalone sales are used to determine the standalone selling price. More frequently, we sell a customized customer specific solution, and in these cases, we typically use the expected cost plus a margin approach to estimate the standalone selling price of each performance obligation.

We recognize revenue over time for all of our services as we perform them because (i) control continuously transfers to that customer as work progresses, and (ii) we have the right to bill the customer as costs are incurred. The customer typically controls the work in process, as evidenced either by contractual termination clauses or by our rights to payment for work performed to date plus a reasonable profit to deliver products or services that do not have an alternative use to the Company.

For the reasons listed above, revenue is recognized based on the extent of progress towards completion of the performance obligation. The selection of the method to measure progress towards completion requires judgment and is based on the nature of the products or services to be provided. We generally use the cost to cost measure of progress for our contracts, as it best depicts the transfer of assets to the customer that occurs as we incur costs on our contracts. Under the cost to cost measure of progress, the extent of progress towards completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation. Revenue, including estimated fees or profits, is recorded proportionally as costs are incurred. Costs to fulfill include labor, materials and subcontractors’ costs, other direct costs and an allocation of indirect costs.

For a small portion of our business in which our services are delivered in the form of service maintenance agreements for existing systems to be repaired and maintained, as opposed to constructed, our performance obligation is to maintain the customer’s mechanical system for a specific period of time. Similar to jobs, we recognize revenue over time; however, for service maintenance agreements in which the full cost to provide services may not be known, we generally use an input method to recognize revenue, which is based on the amount of time we have provided our services out of the total time we have been contracted to perform those services.

Due to the nature of the work required to be performed on many of our performance obligations, the estimation of total revenue and cost at completion (the process described below in more detail) is complex, subject to many variables and requires significant judgment. The consideration to which we are entitled on our long-term contracts may include both fixed and variable amounts. Variable amounts can either increase or decrease the transaction price. A common example of variable amounts that can either increase or decrease contract value are pending change orders that represent contract modifications for which a change in scope has been authorized or acknowledged by our customer, but the final adjustment to contract price is yet to be negotiated. Other examples of positive variable revenue include amounts awarded upon achievement of certain performance metrics, program milestones or cost of completion date targets and can be based upon customer discretion. Variable amounts can result in a deduction from contract revenue if we fail to meet stated performance requirements, such as complying with the construction schedule.

Contracts are often modified to account for changes in contract specifications and requirements. We consider contract modifications to exist when the modification either creates new or changes the existing enforceable rights and obligations. Most of our contract modifications are for goods or services that are not distinct from the existing performance obligation(s). The effect of a contract modification on the transaction price, and our measure of progress for the performance obligation to which it relates, is recognized as an adjustment to revenue (either as an increase or decrease) on a cumulative catchup basis.

We have a Company-wide policy requiring periodic review of the Estimate at Completion in which management reviews the progress and execution of our performance obligations and estimated remaining obligations. As part of this process, management reviews information including, but not limited to, any outstanding key contract matters, progress towards completion and the related program schedule, identified risks and opportunities and the related changes in estimates of revenue and costs. The risks and opportunities include management's judgment about the ability and cost to achieve the schedule (e.g., the number and type of milestone events), technical requirements (e.g., a newly developed product versus a mature product) and other contract requirements. Management must make assumptions and estimates regarding labor productivity and availability, the complexity of the work to be performed, the availability of materials, the length of time to complete the performance obligation (e.g. to estimate increases in wages and prices for materials and related support cost allocations), execution by our subcontractors, the availability and timing of funding from our customer, and overhead cost rates, among other variables.

Based on this analysis, any adjustments to revenue, cost of services, and the related impact to operating income are recognized as necessary in the quarter they become known. These adjustments may result from positive program performance if we determine we will be successful in mitigating risks surrounding the technical, schedule and cost aspects of those performance obligations or realizing related opportunities and may result in an increase in operating income during the performance of individual performance obligations. Likewise, if we determine we will not be successful in mitigating these risks or realizing related opportunities, these adjustments may result in a decrease in operating income. Changes in estimates of revenue, cost of services and the related impact to operating income are recognized quarterly on a cumulative catchup basis, which recognizes in the current period the cumulative effect of the changes on current and prior periods based on a performance obligation's percentage of completion. A significant change in one or more of these estimates could affect the profitability of one or more of our performance obligations. For projects where estimates of total costs to be incurred on a performance obligation exceed total estimates of revenue to be earned, a provision for the entire loss on the performance obligation is recognized in the period the loss is determined.

The Company typically does not incur any returns, refunds, or similar obligations after the completion of the performance obligation since any deficiencies are corrected during the course of the work or are included as a modification to revenue. The Company does offer an industry standard warranty on our work, which is most commonly for a one-year period. The vendors providing the equipment and materials are responsible for any failures in their product unless installed incorrectly. We include an estimated amount to cover estimated warranty expense in our Cost of Services and record a liability on our Balance Sheet to cover our current estimated outstanding warranty obligations.

Prior to implementing ASC 606 on January 1, 2018, our methods for recognizing revenue were very similar to our current method under ASC 606. We used the actual cost as a percent of total expected cost at completion to estimate our percentage complete on fixed price jobs, a mark-up of costs for jobs where revenue was based on time and materials incurred and elapsed time for those service maintenance contracts where the full cost to provide the services cannot be reasonably estimated. Furthermore, our process for allocating transaction price to performance obligations is also substantially similar to prior years where, in most cases, a contract is one performance obligation. In those cases where a contract is determined to have more than one performance obligation, the contract price is allocated to each performance obligation based on its standalone sales price.

During the year ended December 31, 2018, net revenue recognized from our performance obligations satisfied in previous periods was not material.

Disaggregation of Revenue

We disaggregate our revenue from contracts with customers by activity, customer type and contract type, as we believe it best depicts how the nature, amount, timing and uncertainty of our revenue and cash flows are affected by economic factors. Our consolidated 2018 revenue was derived from the following service activities, all of which are in the mechanical services industry, the single industry segment we serve. See details in the following tables (dollars in thousands):


	Year Ended December 31,
Revenue by Service Provided	2018				2017				2016
HVAC and Plumbing	$	1,976,374	90.5	%	$	1,615,468	90.4	%	$	1,462,980	89.5	%
Building Automation Control Systems		95,093	4.4	%		94,041	5.3	%		90,461	5.5	%
Other		111,412	5.1	%		78,413	4.4	%		80,899	4.9	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

	Year Ended December 31,
Revenue by Type of Customer	2018				2017				2016
Industrial	$	596,557	27.3	%	$	395,362	22.1	%	$	378,499	23.2	%
Education		391,937	18.0	%		351,808	19.7	%		307,195	18.8	%
Office Buildings		288,090	13.2	%		248,604	13.9	%		202,187	12.4	%
Healthcare		319,958	14.7	%		224,643	12.6	%		197,797	12.1	%
Government		143,958	6.6	%		140,843	7.9	%		160,414	9.8	%
Retail, Restaurants and Entertainment		225,348	10.3	%		223,593	12.5	%		196,094	12.0	%
Multi-Family and Residential		136,075	6.2	%		116,844	6.5	%		122,766	7.5	%
Other		80,956	3.7	%		86,225	4.8	%		69,388	4.2	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

	Year Ended December 31,
Revenue by Activity Type	2018				2017				2016
New Construction	$	829,978	38.0	%	$	684,687	38.3	%	$	653,488	40.0	%
Existing Building Construction		796,946	36.5	%		580,737	32.4	%		514,437	31.5	%
Service Projects		206,506	9.5	%		197,703	11.1	%		178,455	10.9	%
Service Calls, Maintenance and Monitoring		349,448	16.0	%		324,795	18.2	%		287,960	17.6	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

Accounts Receivable

Accounts Receivable include amounts from work completed in which we have billed or have an unconditional right to bill our customers. The amounts due are stated at their net estimated realizable value. We maintain an allowance for doubtful accounts to provide for the estimated amount of receivables that will not be collected. The allowance is based upon an assessment of customer creditworthiness, historical payment experience, the age of outstanding receivables and collateral to the extent applicable.

Contract Assets and Liabilities

Contract assets include unbilled amounts typically resulting from sales under long term contracts when the cost to cost method of revenue recognition is used and revenue recognized exceeds the amount billed to the customer and right to payment is conditional, subject to completing a milestone, such as a phase of the project. Contract assets are generally classified as current.

Contract liabilities consist of advance payments and billings in excess of revenue recognized. Our contract assets and liabilities are reported in a net position on a contract by contract basis at the end of each reporting period. We classify advance payments and billings in excess of revenue recognized as current. It is very unusual for us to have advanced payments with a term of greater than one year; therefore, our contract assets are usually all current. If we have advanced payments with a term greater than one year, the noncurrent portion of advanced payments would be included in other long-term liabilities in our consolidated balance sheets.

The following table presents the changes in contract assets and contract liabilities (in thousands):


	Year Ended
	December 31, 2018
	Contract		Contract
	Assets		Liabilities
Balance at beginning of period	$	30,116	$	106,005
Change due to acquisitions		2,833		8,195
Change due to conditional versus unconditional		6,244		—
Reclassified to unbilled accounts receivable		(28,980)		—
Change in timing for performance obligation to be satisfied		—		16,786
Balance at December 31, 2018	$	10,213	$	130,986

During the years ended December 31, 2018 and 2017, we recognized revenue of $97.6 million and $86.6 million related to our contract liabilities at January 1, 2018 and January 1, 2017, respectively.

We did not have any impairment losses recognized on our receivables or contract assets in 2018 and 2017.

Remaining Performance Obligations

Remaining construction performance obligations represent the remaining transaction price of firm orders for which work has not been performed and excludes unexercised contract options. As of December 31, 2018, the aggregate amount of the transaction price allocated to remaining performance obligations was $1.17 billion. The Company expects to recognize revenue on approximately 85% of the remaining performance obligations over the next 12 months, with the remaining recognized thereafter. Our service maintenance agreements are generally one-year renewable agreements. We have adopted the practical expedient that allows us to not include service maintenance contracts less than one year, therefore we do not report unfulfilled performance obligations for service maintenance agreements.

Inventories

Inventories consist of parts and supplies that we purchase and hold for use in the ordinary course of business and are stated at the lower of cost or net realizable value using the average-cost method.

Property and Equipment

Property and equipment are stated at cost, and depreciation is computed using the straight‑line method over the estimated useful lives of the assets. Leasehold improvements are capitalized and amortized over the lesser of the expected life of the lease or the estimated useful life of the asset.

Expenditures for repairs and maintenance are charged to expense when incurred. Expenditures for major renewals and betterments, which extend the useful lives of existing equipment, are capitalized and depreciated over the remaining useful life of the equipment. Upon retirement or disposition of property and equipment, the cost and related accumulated depreciation are removed from the accounts and any resulting gain or loss is recognized in “Gain on sale of assets” in the statement of operations.

Recoverability of Goodwill and Identifiable Intangible Assets

Goodwill is the excess of purchase price over the fair value of the net assets of acquired businesses. We assess goodwill for impairment each year, and more frequently if circumstances suggest an impairment may have occurred.

When the carrying value of a given reporting unit exceeds its fair value, a goodwill impairment loss is recorded for this difference, not to exceed the carrying amount of goodwill. If other reporting units have had increases in fair value, such increases may not be recorded. Accordingly, such increases may not be netted against impairments at other reporting units. The requirements for assessing whether goodwill has been impaired involve market‑based information. This information, and its use in assessing goodwill, entails some degree of subjective assessment.

We perform our annual impairment testing as of October 1 and any impairment charges resulting from this process are reported in the fourth quarter. We segregate our operations into reporting units based on the degree of operating and financial independence of each unit and our related management of them. We perform our annual goodwill impairment testing at the reporting unit level. Each of our operating units represents an operating segment, and our operating segments are our reporting units.

In the evaluation of goodwill for impairment, we have the option to first assess qualitative factors to determine whether the existence of events or circumstances lead to a determination that it is more likely than not that the fair value of one of our reporting units is greater than its carrying value. If, after completing such assessment, we determine it is more likely than not that the fair value of a reporting unit is greater than its carrying amount, then there is no need to perform any further testing. If we conclude otherwise, then we calculate the fair value of the reporting unit and compare the fair value with the carrying value of the reporting unit.

We estimate the fair value of the reporting unit based on a market approach and an income approach, which utilizes discounted future cash flows. Assumptions critical to the fair value estimates under the discounted cash flow model include discount rates, cash flow projections, projected long‑term growth rates and the determination of terminal values. The market approach utilizes market multiples of invested capital from comparable publicly traded companies (“public company approach”). The market multiples from invested capital include revenue, book equity plus debt and earnings before interest, provision for income taxes, depreciation and amortization (“EBITDA”).

We amortize identifiable intangible assets with finite lives over their useful lives. Changes in strategy and/or market condition may result in adjustments to recorded intangible asset balances.

Long‑Lived Assets

Long‑lived assets are comprised principally of goodwill, identifiable intangible assets, property and equipment, and deferred tax assets. We periodically evaluate whether events and circumstances have occurred that indicate that the remaining balances of these assets may not be recoverable. We use estimates of future income from operations and cash flows, as well as other economic and business factors, to assess the recoverability of these assets.

Acquisitions

We recognize assets acquired and liabilities assumed in business combinations, including contingent assets and liabilities, based on fair value estimates as of the date of acquisition.

Contingent Consideration—In certain acquisitions, we agree to pay additional amounts to sellers contingent upon achievement by the acquired businesses of certain predetermined profitability targets. We have recognized liabilities for these contingent obligations based on their estimated fair value at the date of acquisition with any differences between the acquisition date fair value and the ultimate settlement of the obligations being recognized in income from operations.

Contingent Assets and Liabilities—Assets and liabilities arising from contingencies are recognized at their acquisition date fair value when their respective fair values can be determined. If the fair values of such contingencies cannot be determined, they are recognized at the acquisition date if the contingencies are probable and an amount can be reasonably estimated. Acquisition date fair value estimates are revised as necessary if, and when, additional information regarding these contingencies becomes available to further define and quantify assets acquired and liabilities assumed.

Self‑Insurance Liabilities

We are substantially self‑insured for workers’ compensation, employer’s liability, auto liability, general liability and employee group health claims, in view of the relatively high per‑incident deductibles we absorb under our insurance arrangements for these risks. Losses are estimated and accrued based upon known facts, historical trends and industry averages. Estimated losses in excess of our deductible, which have not already been paid, are included in our accrual with a corresponding receivable from our insurance carrier. Loss estimates associated with the larger and longer‑developing risks—workers’ compensation, auto liability and general liability—are reviewed by a third‑party actuary quarterly. Our self‑insurance arrangements are further discussed in Note 11 “Commitments and Contingencies.”

Warranty Costs

We typically warrant labor for the first year after installation on new HVAC systems. We generally warrant labor for thirty days after servicing of existing HVAC systems. A reserve for warranty costs is estimated and recorded based upon the historical level of warranty claims and management’s estimate of future costs.

Income Taxes

We conduct business throughout the United States in virtually all fifty states. Our effective tax rate changes based upon our relative profitability, or lack thereof, in states with varying tax rates and rules. In addition, discrete items such as tax law changes, judgments and legal structures can impact our effective tax rate. These items can also include the tax treatment for impairment of goodwill and other intangible assets, changes in fair value of acquisition-related assets and liabilities, tax reserves for uncertain tax positions, accounting for losses associated with underperforming operations and noncontrolling interests.

Income taxes are provided for under the liability method, which takes into account differences between financial statement treatment and tax treatment of certain transactions. Deferred taxes are based on the difference between the financial reporting and tax basis of assets and liabilities. The deferred tax provision represents the change during the reporting period in the deferred tax assets and deferred tax liabilities, net of the effect of acquisitions and dispositions. Deferred tax assets include tax loss and credit carryforwards and are reduced by a valuation allowance if, based on available evidence, it is more-likely-than-not some portion or all of the deferred tax assets will not be realized.

We regularly evaluate valuation allowances established for deferred tax assets for which future realization is uncertain. We perform this evaluation quarterly. In assessing the realizability of deferred tax assets, we must consider whether it is more-likely-than-not some portion, or all, of the deferred tax assets will not be realized. We consider all available evidence, both positive and negative, in determining whether a valuation allowance is required. Such evidence includes the scheduled reversal of deferred tax liabilities, projected future taxable income, taxable income in prior carryback years and tax planning strategies in making this assessment, and judgment is required in considering the relative weight of negative and positive evidence.

Significant judgment is required in assessing the timing and amounts of deductible and taxable items. We establish reserves when, despite our belief that our tax return positions are supportable, we believe that certain positions may be disallowed. When facts and circumstances change, we adjust these reserves through our provision for income taxes.

To the extent interest and penalties may be assessed by taxing authorities on any underpayment of income tax, such amounts have been accrued and are classified as a component in provision for income taxes in our Consolidated Statements of Operations.

Segment Disclosure

Our activities are within the mechanical services industry, which is the single industry segment we serve. Each operating unit represents an operating segment and these segments have been aggregated, as the operating units meet all of the aggregation criteria.

Concentrations of Credit Risk

We provide services in a broad range of geographic regions. Our credit risk primarily consists of receivables from a variety of customers including general contractors, property owners and developers and commercial and industrial companies. We are subject to potential credit risk related to changes in business and economic factors throughout the United States within the nonresidential construction industry. However, we are entitled to payment for work performed and have certain lien rights in that work. Further, we believe that our contract acceptance, billing and collection policies are adequate to manage potential credit risk. We regularly review our accounts receivable and estimate an allowance for uncollectible amounts. We have a diverse customer base, with no single customer accounting for more than 4% of consolidated 2018 revenue.

Financial Instruments

Our financial instruments consist of cash and cash equivalents, accounts receivable, other receivables, accounts payable, life insurance policies, notes to former owners, capital leases, and a revolving credit facility. We believe that the carrying values of these instruments on the accompanying balance sheets approximate their fair values.

Fair Value Measurements

12 Months Ended

Dec. 31, 2018

Fair Value Measurements

Fair Value Measurements

3. Fair Value Measurements

We classify and disclose assets and liabilities carried at fair value in one of the following three categories:

Level 1—quoted prices in active markets for identical assets and liabilities;

Level 2—observable market-based inputs or unobservable inputs that are corroborated by market data; and

Level 3—significant unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions.

The following table summarizes the fair values, and levels within the fair value hierarchy in which the fair value measurements fall, for assets and liabilities measured on a recurring basis as of December 31, 2018 and 2017 (in thousands):


	Fair Value Measurements at December 31, 2018
	Level 1		Level 2		Level 3		Total
Cash and cash equivalents	$	45,620	$	—	$	—	$	45,620
Life insurance—cash surrender value	$	—	$	3,252	$	—	$	3,252
Contingent earn-out obligations	$	—	$	—	$	7,375	$	7,375

	Fair Value Measurements at December 31, 2017
	Level 1		Level 2		Level 3		Total
Cash and cash equivalents	$	36,542	$	—	$	—	$	36,542
Life insurance—cash surrender value	$	—	$	3,128	$	—	$	3,128
Contingent earn-out obligations	$	—	$	—	$	7,993	$	7,993

Cash and cash equivalents consist primarily of highly rated money market funds at a variety of well‑known institutions with original maturities of three months or less. The original cost of these assets approximates fair value due to their short-term maturity. The carrying value of our borrowings associated with the Revolving Credit Facility approximate its fair value due to the variable rate on such debt.

We have life insurance policies covering 58 employees with a combined face value of $42.0 million. The policies are invested in several investment vehicles and the fair value measurement of the cash surrender balance associated with these policies is determined using Level 2 inputs within the fair value hierarchy and will vary with investment performance. The cash surrender value of these policies is $3.3 million as of December 31, 2018 and $3.1 million as of December 31, 2017. These assets are included in “Other Noncurrent Assets” in our consolidated balance sheets.

We value contingent earn‑out obligations using a probability weighted discounted cash flow method. This fair value measurement is based on significant unobservable inputs in the market and thus represents a Level 3 measurement within the fair value hierarchy. This analysis reflects the contractual terms of the purchase agreements (e.g., minimum and maximum payments, length of earn‑out periods, manner of calculating any amounts due, etc.) and utilizes assumptions with regard to future cash flows, probabilities of achieving such future cash flows and a discount rate. The contingent earn‑out obligations are measured at fair value each reporting period and changes in estimates of fair value are recognized in earnings.

The table below presents a reconciliation of the fair value of our contingent earn‑out obligations that use significant unobservable inputs (Level 3) (in thousands).


	December 31,
	2018		2017
Balance at beginning of year	$	7,993	$	2,531
Issuances		4,366		11,755
Settlements		(7,050)		(2,578)
Adjustments to fair value		2,066		(3,715)
Balance at end of year	$	7,375	$	7,993

We measure certain assets at fair value on a nonrecurring basis. These assets are recognized at fair value when they are deemed to be other-than-temporarily impaired. No goodwill or other intangible asset impairments were recorded during the year ended December 31, 2018. During the year ended December 31, 2017, we recorded a goodwill impairment charge of $1.1 million based on Level 3 measurements. We did not recognize any other impairments on those assets required to be measured at fair value on a nonrecurring basis. See Note 5 “Goodwill and Identifiable Intangible Assets, Net” for further discussion.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Acquisitions	12 Months Ended
Acquisitions	Dec. 31, 2018
Acquisitions
Acquisitions	4. Acquisitions We completed two acquisitions in the third quarter of 2018, three acquisitions in the second quarter of 2018 and two acquisitions in the first quarter of 2018, with a total preliminary purchase price of $95.6 million for the year ended December 31, 2018. One acquisition completed in the third quarter of 2018 reports as a separate operating location and the remainder were “tucked-in” with existing operations. Our consolidated balance sheet includes preliminary allocations of the purchase price to the assets acquired and liabilities assumed pending the completion of the final valuation of intangible assets and accrued liabilities. Other Acquisitions In the second quarter of 2017, we acquired all of the issued and outstanding stock of BCH Holdings, Inc. and each of its wholly-owned subsidiaries (collectively “BCH”) for $121.3 million of which $97.0 million was allocated to goodwill and identifiable intangible assets. The total purchase price included $95.4 million in cash, $14.3 million in notes payable to former owners and an $11.6 million contingent earn-out obligation. BCH is an integrated, single-source provider of mechanical service, maintenance and construction with headquarters in Tampa, Florida and operations throughout the southeastern region of the United States, which reports as a separate operating location. In addition to the BCH acquisition, we completed four additional acquisitions in 2017. The total purchase price for these additional acquisitions, including earn-outs, was $9.4 million. We completed two acquisitions in the first quarter of 2016. We acquired the remaining 40% noncontrolling interest in Environmental Air Systems, LLC (“EAS”) on January 1, 2016 for $46.6 million, including $42.0 million funded on the closing date plus a holdback, an earn-out that will be earned if certain financial targets are met after the acquisition date and a working capital adjustment. Due to our majority ownership and control over EAS on the acquisition date, the difference between the purchase price and the noncontrolling interest liability was recorded in Additional Paid-In Capital in our Balance Sheet. Additionally, in the first quarter of 2016, we acquired 100% of the ShoffnerKalthoff family of companies (collectively, “Shoffner”), which reports as a separate operating location in the Knoxville, Tennessee area. The acquisition date fair value of consideration transferred for this acquisition was $19.8 million, of which $14.8 million was allocated to goodwill and identifiable intangible assets. The purchase price included $15.5 million funded on the closing date plus a note payable to former owners, an earn-out that we will pay if certain financial targets are met after the acquisition date and a working capital adjustment. In addition to the EAS and Shoffner acquisitions, we completed one additional acquisition in 2016. The total purchase price for this additional acquisition, including earn-outs, was $0.1 million. The results of operations of acquisitions are included in our consolidated financial statements from their respective acquisition dates. The acquisitions completed in the current and prior year were not material, individually or in the aggregate. Additional contingent purchase price (“earn-out”) has been or will be paid if certain acquisitions achieve predetermined profitability targets. Such earn-outs, when they are not subject to the continued employment of the sellers, are estimated as of the purchase date and included as part of the consideration paid for the acquisition. If we have an earn-out where continued employment is a condition to receive payment, then the earn-out is recorded as compensation expense over the period earned.

Goodwill and Identifiable Intangible Assets, Net

12 Months Ended

Dec. 31, 2018

Goodwill and Identifiable Intangible Assets, Net

Goodwill and Identifiable Intangible Assets, Net

5. Goodwill and Identifiable Intangible Assets, Net

Goodwill

The changes in the carrying amount of goodwill are as follows (in thousands):


	December 31,
	2018		2017
Balance at beginning of year	$	200,584	$	149,208
Additions (See Note 4)		34,598		52,481
Impairment adjustment		—		(1,105)
Balance at end of year	$	235,182	$	200,584

We perform our annual impairment testing on October 1, or more frequently, if events and circumstances indicate impairment may have occurred. As discussed in Note 2, “Summary of Significant Accounting Policies,” we have the option to first perform a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit is less than the carrying value.

During our annual impairment testing on October 1, we performed a qualitative assessment for each reporting unit, which considered various factors, including changes in the carrying value of the reporting unit, forecasted operating results, long-term growth rates and discount rates. Additionally, we considered qualitative key events and circumstances (i.e. macroeconomic environment, industry and market specific conditions, cost factors and events specific to the reporting unit, etc.). Based on this assessment, we concluded that it was more likely than not that the fair value of each of the reporting units was greater than its carrying value. Accordingly, no further testing was required.

We recorded a goodwill impairment charge of $1.1 million during the first quarter of 2017. Based on changes to our market strategy that occurred in March 2017 related to our reporting unit based in California, we reevaluated our projected future earnings for this operating location and determined that we could no longer support the related goodwill balance and therefore the goodwill associated with this location was fully impaired. The fair value was estimated using a discounted cash flow model. The annual impairment test did not identify any additional impairment for 2017.

During 2016, we performed a quantitative assessment where the fair value of each reporting unit was estimated using a discounted cash flow model combined with a market valuation approach. We assigned a weighting of 50% to the discounted cash flow analysis and 50% to the public company approach for the year ended December 31, 2016. Based on this assessment, we concluded that the fair value of each of the reporting units was greater than its carrying value. As of October 1, 2016, the fair value exceeded the carrying value by a significant margin for all of our reporting units with a goodwill balance.

There are significant inherent uncertainties and management judgment involved in estimating the fair value of each reporting unit. While we believe we have made reasonable estimates and assumptions to estimate the fair value of our reporting units, it is possible that a material change could occur. If actual results are not consistent with our current estimates and assumptions, or the current economic outlook worsens, goodwill impairment charges may be recorded in future periods.

Identifiable Intangible Assets, Net

Identifiable intangible assets consist of the following (dollars in thousands):


		December 31,
	Estimated	2018				2017
	Useful Lives	Gross Book		Accumulated		Gross Book		Accumulated
	in Years	Value		Amortization		Value		Amortization
Customer relationships	1 - 15	$	128,480	$	(60,731)	$	98,244	$	(47,057)
Backlog	1 - 2		9,100		(8,260)		6,300		(5,478)
Tradenames	2 - 25		39,395		(12,709)		35,340		(11,305)
Total		$	176,975	$	(81,700)	$	139,884	$	(63,840)

The amounts attributable to customer relationships, noncompete agreements and tradenames are amortized to “Selling, General and Administrative Expenses” on a pattern of economic benefit or a straight‑line method over periods from one to twenty-five years. The amounts attributable to backlog are being amortized to “Cost of Services” on a proportionate method over the remaining backlog period. Amortization expense for the years ended December 31, 2018, 2017 and 2016 was $20.1 million, $17.4 million and $8.2 million, respectively.

At December 31, 2018, future amortization expense of identifiable intangible assets is as follows (in thousands):


Year ended December 31—
2019	$	18,088
2020		15,103
2021		12,060
2022		9,866
2023		8,478
Thereafter		31,680
Total	$	95,275

Property and Equipment

12 Months Ended

Dec. 31, 2018

Property and Equipment

Property and Equipment

6. Property and Equipment

Property and equipment consist of the following (dollars in thousands):


	Estimated
	Useful Lives	December 31,
	in Years	2018		2017
Land	—	$	5,702	$	2,745
Transportation equipment	1 - 7		98,898		87,120
Machinery and equipment	1 - 20		33,907		30,064
Computer and telephone equipment	1 - 10		20,179		20,463
Buildings and leasehold improvements	1 - 40		53,559		38,422
Furniture and fixtures	1 - 17		4,879		4,473
Construction in progress	—		1,715		12,614
			218,839		195,901
Less—Accumulated depreciation			(119,221)		(108,310)
Property and equipment, net		$	99,618	$	87,591

Depreciation expense, including capital lease amortization, for the years ended December 31, 2018, 2017 and 2016 was $22.6 million, $20.1 million and $18.0 million, respectively.

Detail of Certain Balance Sheet Accounts

12 Months Ended

Dec. 31, 2018

Detail of Certain Balance Sheet Accounts

Detail of Certain Balance Sheet Accounts

7. Detail of Certain Balance Sheet Accounts

Activity in our allowance for doubtful accounts consists of the following (in thousands):


	December 31,
	2018		2017		2016
Balance at beginning of year	$	3,400	$	4,288	$	5,158
Bad debt expense (benefit)		3,562		182		(27)
Deductions for uncollectible receivables written off, net of recoveries		(1,304)		(1,829)		(876)
Allowance for doubtful accounts of acquired companies at date of acquisition		240		759		33
Balance at end of year	$	5,898	$	3,400	$	4,288

Other current liabilities consist of the following (in thousands):


	December 31,
	2018		2017
Accrued warranty costs	$	6,453	$	6,149
Accrued job losses		1,495		598
Accrued sales and use tax		2,685		2,308
Deferred revenue		5,233		3,895
Liabilities due to former owners		2,045		2,981
Other current liabilities		14,941		17,723
	$	32,852	$	33,654

Debt Obligations

12 Months Ended

Dec. 31, 2018

Debt Obligations

Debt Obligations

8. Debt Obligations

Debt obligations consist of the following (in thousands):


	December 31,
	2018		2017
Revolving credit facility	$	50,000	$	45,000
Notes to former owners		26,813		15,325
Other debt		105		214
Total debt		76,918		60,539
Less—current portion		(3,279)		(613)
Total long-term portion of debt	$	73,639	$	59,926

At December 31, 2018, future principal payments of debt are as follows (in thousands):


Year ended December 31—
2019	$	3,279
2020		13,822
2021		9,817
2022		—
2023		50,000
	$	76,918

Interest expense included the following primary elements (in thousands):


	Year Ended December 31,
	2018		2017		2016
Interest expense on notes to former owners	$	642	$	365	$	70
Interest expense on borrowings and unused commitment fees		2,211		1,862		1,251
Letter of credit fees		474		553		657
Amortization of debt financing costs		383		376		367
Total	$	3,710	$	3,156	$	2,345

Revolving Credit Facility

On April 18, 2018, we amended our senior credit facility (the “Facility”) provided by a syndicate of banks, increasing our borrowing capacity from $325.0 million to $400.0 million, with a $100 million accordion option. The Facility, which is available for borrowings and letters of credit, expires in April 2023 and is secured by a first lien on substantially all of our personal property except for assets related to projects subject to surety bonds and assets held by certain unrestricted subsidiaries and a second lien on our assets related to projects subject to surety bonds. In 2018, we incurred approximately $0.8 million in financing and professional costs in connection with an amendment to the Facility, which combined with the previous unamortized costs of $1.1 million, are being amortized on a straight-line basis as a non-cash charge to interest expense over the remaining term of the Facility. As of December 31, 2018, we had $50.0 million of outstanding borrowings, $33.6 million in letters of credit outstanding and $316.4 million of credit available.

Collateral

A common practice in our industry is the posting of payment and performance bonds with customers. These bonds are offered by financial institutions known as sureties and provide assurance to the customer that in the event we encounter significant financial or operational difficulties, the surety will arrange for the completion of our contractual obligations and for the payment of our vendors on the projects subject to the bonds. In cooperation with our lenders, we granted our sureties a first lien on assets such as receivables, costs and estimated earnings in excess of billings, and equipment specifically identifiable to projects for which bonds are outstanding, as collateral for potential obligations under bonds. As of December 31, 2018, the book value of these assets was approximately $48.9 million.

Covenants and Restrictions

The Facility contains financial covenants defining various financial measures and the levels of these measures with which we must comply. Covenant compliance is assessed as of each quarter end. Credit Facility Adjusted EBITDA is defined under the Facility for financial covenant purposes as net earnings for the four quarters ending as of any given quarterly covenant compliance measurement date, plus the corresponding amounts for (a) interest expense; (b) provision for income taxes; (c) depreciation and amortization; (d) stock compensation; (e) other non‑cash charges; and (f) pre‑acquisition results of acquired companies. The following is a reconciliation of Credit Facility Adjusted EBITDA to net income for 2018 (in thousands):


Net income	$	112,903
Provision for income taxes		35,773
Interest expense, net		3,637
Depreciation and amortization expense		42,689
Stock-based compensation		7,161
Pre-acquisition results of acquired companies, as defined under the Facility		3,771
Credit Facility Adjusted EBITDA	$	205,934

The Facility’s principal financial covenants include:

Total Leverage Ratio—The Facility requires that the ratio of our Consolidated Total Indebtedness to our Credit Facility Adjusted EBITDA not exceed 3.00 to 1.00 as of the end of each fiscal quarter. The leverage ratio as of December 31, 2018 was 0.4.

Fixed Charge Coverage Ratio—The Facility requires that the ratio of (a) Credit Facility Adjusted EBITDA, less non-financed capital expenditures, provision for income taxes, dividends and amounts used to repurchase stock to (b) the sum of interest expense and scheduled principal payments of indebtedness be at least 2.00 to 1.00; provided that the calculation of the fixed charge coverage ratio excludes stock repurchases and the payment of dividends at any time that the Company’s Net Leverage Ratio, as defined in the credit agreement, does not exceed 1.75 to 1.00. The Facility also allows the fixed charge coverage ratio not to be reduced for stock repurchases made after the effective date of the Facility in an aggregate amount not to exceed $30 million, if at the time of and after giving effect to such repurchase the Company’s Net Leverage Ratio was less than or equal to 1.75 to 1.00. Credit Facility Adjusted EBITDA, capital expenditures, provision for income taxes, dividends, stock repurchase payments, interest expense, and scheduled principal payments are defined under the Facility for purposes of this covenant to be amounts for the four quarters ending as of any given quarterly covenant compliance measurement date. The fixed charge coverage ratio as of December 31, 2018 was 21.9.

Other Restrictions—The Facility permits acquisitions of up to $40.0 million per transaction, provided that the aggregate purchase price of such an acquisition and of acquisitions in the same fiscal year does not exceed $80.0 million. However, these limitations only apply when the Company’s Net Leverage Ratio is equal to or greater than 2.00 to 1.00.

While the Facility’s financial covenants do not specifically govern capacity under the Facility, if our debt level under the Facility at a quarter‑end covenant compliance measurement date were to cause us to violate the Facility’s leverage ratio covenant, our borrowing capacity under the Facility and the favorable terms that we currently have could be negatively impacted by the lenders.

We were in compliance with all of our financial covenants as of December 31, 2018.

Interest Rates and Fees

There are two interest rate options for borrowings under the Facility, the Base Rate Loan Option and the Eurodollar Rate Loan Option. Additional margins are then added to these two rates. Under the Base Rate Loan Option, the interest rate is determined based on the highest of the Federal Funds Rate plus 0.5%, the prime lending rate offered by Wells Fargo Bank, N.A. or the one‑month Eurodollar Rate plus 1.00%. Under the Eurodollar Rate Loan Option, the interest rate is determined based on the one‑ to six‑month Eurodollar Rate. The Eurodollar Rate corresponds very closely to rates described in various general business media sources as the London Interbank Offered Rate or “LIBOR.” Additional margins are then added to these rates. The additional margins are determined based on the ratio of our Consolidated Total Indebtedness as of a given quarter end to our “Credit Facility Adjusted EBITDA” for the twelve months ending as of that quarter end, as defined in the credit agreement and shown below.

The interest rates under the Facility are floating rates determined by the broad financial markets, meaning they can and do move up and down from time to time. For illustrative purposes, the following are the respective market rates as of December 31, 2018 relating to interest options under the Facility:


Base Rate Loan Option:
Federal Funds Rate plus 0.50%		2.95%
Wells Fargo Bank, N.A. Prime Rate		5.50%
One-month LIBOR plus 1.00%		3.52%
Eurodollar Rate Loan Option:
One-month LIBOR		2.52%
Six-month LIBOR		2.87%

Certain of our vendors require letters of credit to ensure reimbursement for amounts they are disbursing on our behalf, such as to beneficiaries under our self‑funded insurance programs. We have also occasionally used letters of credit to guarantee performance under our contracts and to ensure payment to our subcontractors and vendors under those contracts. Our lenders issue such letters of credit through the Facility. A letter of credit commits the lenders to pay specified amounts to the holder of the letter of credit if the holder demonstrates that we have failed to perform specified actions. If this were to occur, we would be required to reimburse the lenders for amounts they fund to honor the letter of credit holder’s claim. Absent a claim, there is no payment or reserving of funds by us in connection with a letter of credit. However, because a claim on a letter of credit would require immediate reimbursement by us to our lenders, letters of credit are treated as a use of facility capacity just the same as actual borrowings. We have never had a claim made against a letter of credit that resulted in payments by a lender or by us and believe such claim is unlikely in the foreseeable future.

Commitment fees are payable on the portion of the revolving loan capacity not in use for borrowings or letters of credit at any given time. Letter of credit fees and commitment fees are based on the ratio of Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA, as defined in the credit agreement.


	Consolidated Total Indebtedness to
	Credit Facility Adjusted EBITDA
	Less than 1.00		1.00 to 1.75		1.75 to 2.50		2.50 or greater
Additional Per Annum Interest Margin Added Under:
Base Rate Loan Option	0.25	%	0.50	%	0.75	%	1.00	%
Eurodollar Rate Loan Option	1.25	%	1.50	%	1.75	%	2.00	%
Letter of credit fees	1.25	%	1.50	%	1.75	%	2.00	%
Commitment fees on any portion of the Revolving Loan capacity not in use for borrowings or letters of credit at any given time	0.20	%	0.25	%	0.30	%	0.35	%

The weighted average interest rate applicable to the borrowings under the Facility was approximately 3.7% as of December 31, 2018.

Notes to Former Owners

As part of the consideration used to acquire six companies, we have outstanding notes to the former owners. These notes had an outstanding balance of $26.8 million as of December 31, 2018. In conjunction with an acquisition in the third quarter of 2018, we issued a promissory note to the former owners with an outstanding balance of $6.5 million as of December 31, 2018 that bears interest, payable quarterly, at a weighted average interest rate of 3.5%. The principal is due in three equal installments in July 2019, 2020 and 2021. In conjunction with a separate acquisition in the third quarter of 2018, we issued a promissory note to former owners with an outstanding balance of $3.5 million as of December 31, 2018 that bears interest, payable quarterly, at a weighted average interest rate of 2.9%. The principal is due in September 2020. In conjunction with a small acquisition in the second quarter of 2018, we issued a subordinated note to former owners with an outstanding balance of $1.0 million as of December 31, 2018 that bears interest, payable quarterly, at a weighted average interest rate of 3.5%. The principal is due in equal installments in May 2020 and 2021. In conjunction with a small acquisition in the first quarter of 2018, we issued a subordinated note to former owners with an outstanding balance of $1.0 million as of December 31, 2018 that bears interest, payable quarterly, at a weighted average interest rate of 2.5%. The principal is due in equal installments in January 2019 and 2020. In conjunction with the BCH acquisition in the second quarter of 2017, we issued a promissory note to former owners with an outstanding balance of $14.3 million as of December 31, 2018 that bears interest, payable quarterly, at a weighted average interest rate of 3.0%. The principal is due in equal installments in April 2020 and 2021. In conjunction with the Shoffner acquisition in the first quarter of 2016, we issued a subordinated note to former owners with an outstanding balance of $0.5 million as of December 31, 2018 that bears interest, payable quarterly, at a weighted average interest rate of 3.0%. The principal is due in February 2019.

Other Debt

As part of the Shoffner acquisition, we acquired debt with an outstanding balance at the acquisition date of $0.4 million with principal and interest due the last day of every month; ending on the December 30, 2019 maturity date. The interest rate is the one month LIBOR rate plus 2.25%. As of December 31, 2018, $0.1 million of the note was outstanding, all of which was considered current.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Taxes

Income Taxes

9. Income Taxes

Provision for Income Taxes

Our provision for income taxes relating to continuing operations consists of the following (in thousands):


	December 31,
	2018		2017		2016
Current tax provision—
Federal	$	22,728	$	35,434	$	32,721
State and Puerto Rico		8,589		6,054		4,683
Total current		31,317		41,488		37,404
Deferred tax provision (benefit)—
Federal		4,347		5,391		(2,101)
State and Puerto Rico		109		(1,213)		862
Total deferred		4,456		4,178		(1,239)
Provision for income taxes	$	35,773	$	45,666	$	36,165

The provision for income taxes for the years ended December 31, 2018, 2017 and 2016 resulted in effective tax rates on continuing operations of 24.1%, 45.2% and 35.8%, respectively. The reasons for the differences between these effective tax rates and the federal statutory rates are as follows (in thousands):


	December 31,
	2018			2017			2016
Federal statutory rate of—		21	%		35	%		35	%
Income taxes at the federal statutory rate	$	31,222		$	35,328		$	35,371
Increases (decreases) resulting from—
Net state income taxes		7,470			2,838			4,262
Valuation allowances		(2,852)			91			(1,254)
Net unrecognized tax benefits		(15)			153			20
Nondeductible expenses		1,926			1,134			825
R&D tax credits		(2,726)			—			—
Net operating loss carryforwards		2,225			—			—
Stock-based compensation deductions		(1,293)			(1,320)			(885)
Domestic production activities deduction		—			(2,112)			(2,026)
Corporate tax rate reduction to 21%		—			9,478			—
Other		(184)			76			(148)
Provision for income taxes	$	35,773		$	45,666		$	36,165

As of December 31, 2017, we recorded provisional amounts for the impact of the Tax Cuts and Jobs Act. An expense of $9.5 million was recorded in the fourth quarter of 2017 for the remeasurement of our net deferred tax assets based on the rates at which they are expected to reverse in the future (generally 21%). At December 31, 2018, we completed our accounting for the impact of the Tax Cuts and Jobs Act, and no further adjustments were made.

During 2018, we filed an amended return claiming the credit for increasing research activities (“R&D tax credits”) and recorded a $2.7 million tax benefit that was fully offset by an increase in unrecognized tax benefits. We also dissolved our Puerto Rican subsidiary and thus wrote-off the remaining $2.2 million of net operating loss (“NOL”) carryforwards and related valuation allowance. Neither the R&D tax credits claim nor the dissolution of our Puerto Rican subsidiary had an impact on our 2018 effective tax rate.

Deferred Tax Assets (Liabilities)

Significant components of the deferred tax assets and deferred tax liabilities as reflected on the balance sheets are as follows (in thousands):


	Year Ended
	December 31,
	2018		2017
Deferred tax assets—
Accounts receivable and allowance for doubtful accounts	$	1,445	$	715
Stock-based compensation		2,538		2,297
Accrued liabilities and expenses		19,449		19,555
Net operating loss carryforwards		3,242		6,007
Intangible assets		5,071		2,272
Other		550		544
Subtotal		32,295		31,390
Valuation allowances		(648)		(3,500)
Total deferred tax assets		31,647		27,890
Deferred tax liabilities—
Property and equipment		(10,488)		(4,668)
Long-term contracts		(688)		(625)
Goodwill		(3,864)		(1,572)
Other		(360)		(322)
Total deferred tax liabilities		(15,400)		(7,187)
Net deferred tax assets	$	16,247	$	20,703

The deferred tax assets and liabilities reflected above are included in the consolidated balance sheets as follows (in thousands):


	December 31,
	2018		2017
Deferred tax assets	$	17,634	$	22,966
Deferred tax liabilities	$	1,387	$	2,263

As of December 31, 2018, we had $3.2 million of future tax benefits related to $55.5 million of available state NOL carryforwards, which expire in varying amounts between the years 2021 and 2038. Valuation allowances of $0.6 million have been recorded against certain of the state NOL carryforwards. The $2.6 million deferred tax asset for state NOL carryforwards, net of valuation allowances, reflects our conclusion that it is more-likely-than-not these assets will be realized based upon expected future earnings in certain subsidiaries.

We update our assessment of the realizability of deferred tax assets relating to state NOL carryforwards annually. A return to profitability in our subsidiaries with valuation allowances would result in a release of a portion of the valuation allowance relating to realizable deferred tax assets. A sustained period of profitability could cause a change in our judgment of any remaining deferred tax assets. If that were to occur, then it is likely that we would reverse some or all of the remaining valuation allowances.

Liabilities for Uncertain Tax Positions

A reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding accrued interest and penalties, is as follows (in thousands):


	Year Ended
	December 31,
	2018		2017		2016
Balance at beginning of year	$	8,929	$	240	$	240
Additions based on tax positions related to current year		—		8,689		—
Additions based on tax positions related to prior years		2,726		—		—
Reductions for tax positions related to prior years		(8,689)		—		—
Reductions for settlements with tax authorities		—		—		—
Balance at end of year	$	2,966	$	8,929	$	240

As of December 31, 2018, 2017 and 2016, we had $3.0 million, $8.9 million and $0.2 million, respectively, of unrecognized tax benefits, which if recognized in future periods, would impact our effective tax rate. We also had accrued $0.6 million, $0.7 million and $0.4 million for potential interest and penalties related to the unrecognized tax benefits as of December 31, 2018, 2017 and 2016, respectively. We recognize potential interest and penalties related to unrecognized tax benefits in our provision for income taxes.

We believe it is reasonably possible that a decrease of up to $3.0 million in unrecognized tax benefits could occur within the next twelve months. Any decrease in our unrecognized tax benefits, due to the future recognition of those tax benefits, would affect our effective tax rate.

We are subject to taxation in the United States and various state jurisdictions. In the fourth quarter of 2017, we received a ‘no change letter’ from the Internal Revenue Service upon completion of its examination of the 2015 tax year. We remain open to examination by various state tax authorities for the 2010 tax year forward. As of December 31, 2018, we did not have any state audits underway that would have a material impact on our financial position or results of operations.

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2018
Employee Benefit Plans
Employee Benefit Plans	10. Employee Benefit Plans We and certain of our subsidiaries sponsor various retirement plans for most full‑time and some part‑time employees. These plans primarily consist of defined contribution plans. The defined contribution plans generally provide for contributions up to 2.5% of covered employees’ salaries or wages. These contributions totaled $10.8 million in 2018, $7.8 million in 2017 and $7.8 million in 2016. Of these amounts, approximately $0.2 million and $0.5 million were payable to the plans at December 31, 2018 and 2017, respectively. Certain of our subsidiaries also participate or have participated in various multi‑employer pension plans for the benefit of employees who are union members. As of December 31, 2018 and 2017, we had 6 and 6, respectively, who were union members. There were no contributions made to multi‑employer pension plans in 2018, 2017 or 2016. The data available from administrators of other multi‑employer pension plans is not sufficient to determine the accumulated benefit obligations, nor the net assets attributable to the multi‑employer plans in which our employees participate or previously participated. Certain individuals at one of our operating units are entitled to receive fixed annual payments that reach a maximum amount, as specified in the related agreements, for a 15 year period following retirement or, in some cases, the attainment of 65 years of age. We recognize the unfunded status of the plan as a non‑current liability in our Consolidated Balance Sheet. Benefits vest 50% after ten years of service, 75% after fifteen years of service and are fully vested after 20 years of service. We had an unfunded benefit liability of $4.3 million and $4.0 million recorded as of December 31, 2018 and 2017.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies

Commitments and Contingencies

11. Commitments and Contingencies

Leases

We lease certain facilities and equipment under noncancelable operating leases. Rent expense for the years ended December 31, 2018, 2017 and 2016 was $23.4 million, $21.1 million, and $20.6 million, respectively. We recognize escalating rental payments that are quantifiable at the inception of the lease on a straight‑line basis over the lease term. Concurrent with the acquisitions of certain companies, we entered into various agreements with previous owners to lease buildings used in our operations. The terms of these leases generally range from three to ten years and certain leases provide for escalations in the rental expenses each year, the majority of which are based on inflation. Included in the 2018, 2017 and 2016 rent expense above are approximately $4.8 million, $4.8 million and $5.1 million of rent paid to these related parties, respectively.

The following represents future minimum rental payments under noncancelable operating leases (in thousands):


Year ended December 31—
2019	$	13,503
2020		10,768
2021		9,449
2022		7,707
2023		6,402
Thereafter		28,328
	$	76,157

Claims and Lawsuits

We are subject to certain legal and regulatory claims, including lawsuits arising in the normal course of business. We maintain various insurance coverages to minimize financial risk associated with these claims. We have estimated and provided accruals for probable losses and related legal fees associated with certain litigation in the accompanying consolidated financial statements. While we cannot predict the outcome of these proceedings, in management’s opinion and based on reports of counsel, any liability arising from these matters individually and in the aggregate will not have a material effect on our operating results, cash flows or financial condition, after giving effect to provisions already recorded.

In April 2018, we entered into settlement agreements with British Petroleum (“BP”) related to two claims from one of our subsidiaries regarding the April 2010 BP Deepwater Horizon oil spill. We recorded a gain of $4.0 million in the second quarter of 2018 in “Other Income” as a result of these settlements. In the fourth quarter of 2017, we entered into settlement agreements with BP related to two claims from another one of our subsidiaries. We recorded a $1.0 million gain in the fourth quarter of 2017 in “Other Income” as a result of these settlements. Additionally, in the fourth quarter of 2016, we entered into a separate settlement agreement with BP related to a claim from another one of our subsidiaries and recorded a $0.6 million gain in the fourth quarter of 2016 in “Other Income”. We do not have any remaining subsidiaries with outstanding claims against BP related to this matter.

Surety

Many customers, particularly in connection with new construction, require us to post performance and payment bonds issued by a financial institution known as a surety. If we fail to perform under the terms of a contract or to pay subcontractors and vendors who provided goods or services under a contract, the customer may demand that the surety make payments or provide services under the bond. We must reimburse the surety for any expenses or outlays it incurs. To date, we are not aware of any losses to our sureties in connection with bonds the sureties have posted on our behalf, and do not expect such losses to be incurred in the foreseeable future.

Surety market conditions have seen some strengthening as the commercial construction markets have started to rebound. Bonding capacity remains adequate in the current market conditions along with acceptable terms and conditions. Historically, approximately 20% to 30% of our business has required bonds. While we currently have strong surety relationships to support our bonding needs, future market conditions or changes in the sureties’ assessment of our operating and financial risk could cause the sureties to decline to issue bonds for our work. If that were to occur, the alternatives include doing more business that does not require bonds, posting other forms of collateral for project performance such as letters of credit or cash, and seeking bonding capacity from other sureties. We would likely also encounter concerns from customers, suppliers and other market participants as to our creditworthiness. While we believe our general operating and financial characteristics would enable us to ultimately respond effectively to an interruption in the availability of bonding capacity, such an interruption would likely cause our revenue and profits to decline in the near term.

Self‑Insurance

We are substantially self‑insured for workers’ compensation, employer’s liability, auto liability, general liability and employee group health claims, in view of the relatively high per‑incident deductibles we absorb under our insurance arrangements for these risks. Losses are estimated and accrued based upon known facts, historical trends and industry averages. Estimated losses in excess of our deductible, which have not already been paid, are included in our accrual with a corresponding receivable from our insurance carrier. Loss estimates associated with the larger and longer‑developing risks, such as workers’ compensation, auto liability and general liability, are reviewed by a third‑party actuary quarterly.

Our self‑insurance arrangements as of December 31, 2018 were as follows:

Workers’ Compensation—The per‑incident deductible for workers’ compensation is $1.0 million. Losses above $1.0 million are determined by statutory rules on a state‑by‑state basis and are fully covered by excess workers’ compensation insurance.

Employer’s Liability—For employer’s liability, the per-incident deductible is $1.0 million and then we have several layers of excess loss insurance policies that cover losses up to $100.0 million in aggregate across this risk area (as well as general liability and auto liability noted below).

General Liability—For general liability, the per-incident deductible is $1.0 million. We are fully insured for the next $1.0 million of each loss, and then have several layers of excess loss insurance policies that cover losses up to $100.0 million in aggregate across this risk area (as well as employer’s liability noted above and auto liability noted below).

Auto Liability—For auto liability, the per-incident deductible is $0.5 million. We are fully insured for the next $1.5 million of each loss, and then have several layers of excess loss insurance policies that cover losses up to $100.0 million in aggregate across this risk area (as well as employer’s liability and general liability noted above).

Employee Medical—We have three medical plans. The deductible for employee group health claims is $350,000 per person, per policy (calendar) year for each plan. Insurance then covers any responsibility for medical claims in excess of the deductible amount.

Our $100.0 million of aggregate excess loss coverage above applicable per‑incident deductibles represents one policy limit that applies to all lines of risk; we do not have a separate $100.0 million of excess loss coverage for each of general liability, employer’s liability and auto liability.

Stockholders' Equity

12 Months Ended

Dec. 31, 2018

Stockholders' Equity

Stockholders' Equity

12. Stockholders’ Equity

2012 Equity Incentive Plan

In May 2012, our stockholders approved our 2012 Equity Incentive Plan (the “2012 Plan”), which provides for the granting of incentive or non‑qualified stock options, stock appreciation rights, restricted or deferred stock, dividend equivalents or other incentive awards to directors, employees, or consultants. The number of shares authorized and reserved for issuance under the 2012 Plan is 5.1 million shares. As of December 31, 2018, there were 2.9 million shares available for issuance under this plan; however, following adoption of the 2017 Plan (described below), no additional shares will be issued under the 2012 Plan. The 2012 Plan will expire in May 2022.

2017 Omnibus Incentive Plan

In May 2017, our stockholders approved our 2017 Omnibus Incentive Plan (the “2017 Plan”), which provides for the granting of incentive or non‑qualified stock options, stock appreciation rights, restricted or deferred stock, dividend equivalents or other incentive awards to directors, employees, or consultants. The number of shares authorized and reserved for issuance under the 2017 Plan is 2.9 million shares. As of December 31, 2018, there were 2.6 million shares available for issuance under this plan. The 2017 Plan will expire in May 2027. Additionally, we have outstanding stock options, stock awards and stock units that were issued under other plans, and no further grants may be made under those plans.

Share Repurchase Program

On March 29, 2007, our Board of Directors (the “Board”) approved a stock repurchase program to acquire up to 1.0 million shares of our outstanding common stock. Subsequently, the Board has from time to time increased the number of shares that may be acquired under the program and approved extensions of the program. Since the inception of the repurchase program, the Board has approved 8.8 million shares to be repurchased. As of December 31, 2018, we have repurchased a cumulative total of 8.2 million shares at an average price of $16.24 per share under the repurchase program.

The share repurchases will be made from time to time at our discretion in the open market or privately negotiated transactions as permitted by securities laws and other legal requirements, and subject to market conditions and other factors. The Board may modify, suspend, extend or terminate the program at any time. During the twelve months ended December 31, 2018, we repurchased 0.6 million shares for approximately $28.5 million at an average price of $48.13 per share.

Earnings Per Share

Basic earnings per share (“EPS”) is computed by dividing net income by the weighted average number of shares of common stock outstanding during the year. Diluted EPS is computed considering the dilutive effect of stock options, restricted stock, restricted stock units and performance stock units. The vesting of unvested contingently issuable performance stock units is based on the achievement of certain earnings per share targets and total shareholder return. These shares are considered contingently issuable shares for purposes of calculating diluted earnings per share. These shares are not included in the diluted earnings per share denominator until the performance criteria are met, if it is assumed that the end of the reporting period was the end of the contingency period.

Unvested restricted stock, restricted stock units and performance stock units are included in diluted earnings per share, weighted outstanding until the shares and units vest. Upon vesting, the vested restricted stock, restricted stock units and performance stock units are included in basic earnings per share weighted outstanding from the vesting date.

There were less than 0.1 million anti-dilutive stock options excluded from the calculation of diluted EPS for the year ended December 31, 2018 and 2017, respectively. There were approximately 0.1 million anti-dilutive stock options excluded from the calculation of diluted EPS for the year ended December 31, 2016.

The following table reconciles the number of shares outstanding with the number of shares used in computing basic and diluted earnings per share for each of the periods presented (in thousands):



	Year Ended December 31,
	2018	2017	2016
Common shares outstanding, end of period	36,894	37,187	37,209
Effect of using weighted average common shares outstanding	308	52	126
Shares used in computing earnings per share—basic	37,202	37,239	37,335
Effect of shares issuable under stock option plans based on the treasury stock method	283	316	330
Effect of restricted and contingently issuable shares	107	117	146
Shares used in computing earnings per share—diluted	37,592	37,672	37,811

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

Stock-Based Compensation

Stock-Based Compensation

13. Stock‑Based Compensation

Grants of stock options, restricted stock and restricted stock units, and performance share units have been, under the 2012 Plan, and under the 2017 Omnibus Incentive Plan (the “2017 Plan”), determined and administered by the compensation committee of the Board of Directors. Total stock‑based compensation expense was $7.2 million, $6.4 million and $5.0 million for the years ended December 31, 2018, 2017 and 2016, respectively. Stock-based compensation expense is recognized using the straight‑line method over the vesting period and generally vests over a three‑year vesting period. Certain awards provide for accelerated vesting when the sum of an employee's age and years of service is at least 75. We recognize forfeitures as they occur. Total income tax benefit recognized for stock‑based compensation arrangements was $1.5 million, $2.4 million and $1.9 million for each of the years ended December 31, 2018, 2017 and 2016.

We generally issue treasury shares for stock options and restricted stock, unless treasury shares are not available. Upon the vesting of restricted shares, we have allowed the holder to elect to surrender an amount of shares to meet their statutory tax withholding requirements. These shares are accounted for as treasury stock based upon the value of the stock on the date of vesting.

Stock Options

The following table summarizes activity under our stock option plans (shares in thousands):


	Year Ended
	December 31,
	2018
		Weighted-
		Average
Stock Options	Shares	Exercise Price
Outstanding at beginning of year	630	$	20.03
Granted	87	$	42.50
Exercised	(207)	$	15.01
Forfeited	(11)	$	38.08
Expired	—	$	—
Outstanding at end of year	499	$	25.65
Options exercisable at end of year	336

The total intrinsic value of options exercised during the years ended December 31, 2018, 2017 and 2016 was $6.7 million, $3.6 million and $1.9 million, respectively. Stock options exercisable as of December 31, 2018 have a weighted‑average remaining contractual term of 5.4 years and an aggregate intrinsic value of $8.1 million. As of December 31, 2018, we have 0.5 million options that are vested or expected to vest; these options have a weighted average exercise price of $25.65 per share, have a weighted‑average remaining contractual term of 6.4 years and an aggregate intrinsic value of $9.0 million.

The following table summarizes information about stock options outstanding at December 31, 2018 (shares in thousands):


	Options Outstanding				Options Exercisable
		Weighted-
		Average
	Number	Remaining	Weighted-		Number	Weighted-
	Outstanding at	Contractual	Average		Exercisable at	Average
Range of Exercise Prices	12/31/2018	Life	Exercise Price		12/31/2018	Exercise Price
$11.00 - $15.00	109	3.54	$	13.61	109	$	13.61
$15.01 - $20.00	158	5.70	$	17.83	158	$	17.83
$20.01 - $36.25	232	8.24	$	36.58	69	$	32.38
$11.00 - $36.25	499	6.41	$	25.65	336	$	19.46

The fair value of each option award is estimated, based on several assumptions, on the date of grant using the Black‑Scholes option valuation model. The fair values and the assumptions used for the 2018, 2017 and 2016 grants are shown in the table below:


	Year Ended December 31,
	2018		2017		2016
Weighted-average fair value per share of options granted	$	13.06	$	11.43	$	9.94
Fair value assumptions:
Expected dividend yield		0.79%		0.89%		0.97%
Expected stock price volatility		31.7%		34.5%		37.9%
Risk-free interest rate		2.66%		2.11%		1.41%
Expected term		5.3 years		5.3 years		5.3 years

Stock options are accounted for as equity instruments. As of December 31, 2018, the unrecognized compensation cost related to stock options was $0.2 million, which is expected to be recognized over a weighted‑average period of 1.6 years. The total fair value of options vested during the year ended December 31, 2018 was $0.9 million.

The following table summarizes information about nonvested stock option awards as of December 31, 2018 and changes for the year ended December 31, 2018 (shares in thousands):


		Weighted-Average
		Grant Date
Stock Options	Shares	Fair Value
Nonvested at December 31, 2017	186	$	9.85
Granted	87	$	13.06
Vested	(99)	$	8.91
Forfeited	(11)	$	11.92
Nonvested at December 31, 2018	163	$	11.99

Restricted Stock and Restricted Stock Units

The following table summarizes activity under our restricted stock plans (shares in thousands):


	Year Ended
	December 31,
	2018
		Weighted
		Average Grant
Restricted Stock and Restricted Stock Units	Shares	Date Fair Value
Unvested at beginning of year	92	$	30.48
Granted	69	$	44.02
Vested	(77)	$	34.17
Forfeited	(6)	$	40.01
Unvested at end of year	78	$	38.17

Approximately $0.7 million of compensation expense related to restricted stock and restricted stock units will be recognized over a weighted‑average period of 1.7 years. The total fair value of shares vested during the year ended December 31, 2018 was $2.6 million. The weighted‑average fair value per share of restricted stock shares and units awarded during 2018, 2017 and 2016 was $44.02, $35.69 and $30.25, respectively. The aggregate intrinsic value of restricted stock vested during the years ended December 31, 2018, 2017 and 2016 was $3.3 million, $3.2 million and $3.6 million, respectively.

Performance Stock Units

Under the 2012 Plan, we granted dollar‑denominated performance vesting restricted stock units (“PSUs”), which cliff vest at the end of a three‑year performance period. The PSUs are subject to two performance measures; 50% of the PSUs are based on the annual performance of our stock price relative to a group of our peers (total shareholder return) and 50% of the PSUs are measured based on meeting or exceeding a pre‑determined annual earnings per share target as set by our board of directors (EPS). Depending on the Company’s performance in relation to the established performance measures, the awards may vest at zero to a maximum of 2.0 times the dollar‑denominated award granted at target. Upon achievement of the necessary performance metrics, the award will be determined in dollars and may be settled in cash or stock based on the market price of the Company’s common stock at the end of the performance period, at our discretion.

Compensation expense for dollar‑denominated performance units will ultimately be equal to the final dollar value awarded to the grantee upon vesting, settled either in cash or stock. However, throughout the performance period we must record and accrue expense based on an estimate of that future payout. For units determined by EPS performance, the awards are evaluated quarterly against established targets in order to estimate the liability throughout the vesting period. For units determined by total shareholder return performance, a Monte Carlo simulation model was used to estimate accruals throughout the vesting period. The model simulates our total shareholder return and compares it against our peer group over the three‑year performance period to produce a predicted distribution of relative share performance. This is applied to the reward criteria to give an expected value of the total shareholder return element. The calculated fair market value as of December 31, 2018 was $5.3 million. Of this amount, $2.1 million relates to the PSUs granted in 2016 whose performance period ended December 31, 2018. These awards will be settled within the upcoming year either in cash or stock. The expense related to performance stock units for the years ended December 31, 2018, 2017 and 2016 was $2.9 million, $2.6 million and $1.6 million, respectively. At the December 31, 2018 calculated fair market value, approximately $0.4 million of compensation expense related to performance stock units will be recognized over a weighted‑average period of 1.2 years.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2018

Selected Quarterly Financial Data (Unaudited)

Selected Quarterly Financial Data (Unaudited)

14. Selected Quarterly Financial Data (Unaudited)

Quarterly financial information for the years ended December 31, 2018 and 2017 is summarized as follows (in thousands, except per share data):


	2018
	Q1		Q2		Q3		Q4
Revenue	$	464,941	$	535,043	$	594,536	$	588,359
Gross profit		89,053		111,183		127,868		118,175
Net income		16,659		32,547		38,541		25,156
INCOME PER SHARE:
Basic	$	0.45	$	0.87	$	1.03	$	0.68
Diluted	$	0.44	$	0.87	$	1.02	$	0.67


	2017
	Q1		Q2		Q3		Q4
Revenue	$	380,588	$	465,411	$	480,851	$	461,072
Gross profit		75,954		95,738		100,858		93,731
Net income (1)		7,477		17,972		22,284		7,539
INCOME PER SHARE:
Basic	$	0.20	$	0.48	$	0.60	$	0.20
Diluted	$	0.20	$	0.48	$	0.59	$	0.20

(1)

In the fourth quarter of 2017, we recorded a $9.5 million increase to the provision for income taxes to remeasure our net deferred tax assets for the enacted corporate tax rate reduction.

The sums of the individual quarterly earnings per share amounts do not necessarily agree with year‑to‑date earnings per share as each quarter’s computation is based on the weighted average number of shares outstanding during the quarter, the weighted average stock price during the quarter and the dilutive effects of options and contingently issuable restricted stock in each quarter.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2018
Subsequent Events
Subsequent Events	15. Subsequent Events In February 2019, we signed a definitive agreement, pending customary closing conditions, to acquire all of the issued and outstanding stock of Walker TX Holding Company, Inc. and each of its wholly-owned subsidiaries (collectively “Walker”). We expect the transaction to close early in the second quarter of 2019. The purchase price consists of $178 million in cash at closing, subject to working capital and certain other post-closing adjustments as set forth in the purchase agreement, and $25 million in a promissory note that is payable in two equal installments of $12.5 million on the third and fourth anniversaries of the closing date, plus an earn out that we will pay if certain financial targets are met after the acquisition date. Walker is a full-service electrical contracting and network infrastructure engineering business serving commercial and industrial clients with headquarters in Irving, Texas and operations throughout the state of Texas.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Principles of Consolidation

Use of Estimates

Cash Flow Information

We consider all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.

Cash paid (in thousands) for:


	Year Ended December 31,
	2018		2017		2016
Interest	$	3,743	$	2,832	$	1,864
Income taxes	$	33,401	$	38,144	$	29,349

Recent Accounting Pronouncements

Revenue Recognition

Contracts in progress are as follows (in thousands):


	December 31,
	2018		2017
Costs incurred on contracts in progress	$	1,574,460	$	1,288,330
Estimated earnings, net of losses		300,514		253,641
Less—Billings to date		(1,958,567)		(1,617,860)
Less—Unbilled accounts receivable		(37,180)		—
	$	(120,773)	$	(75,889)

Costs and estimated earnings in excess of billings	$	10,213	$	30,116
Billings in excess of costs and estimated earnings		(130,986)		(106,005)
	$	(120,773)	$	(75,889)

Variations from estimated project costs could have a significant impact on our operating results, depending on project size, and the recoverability of the variation via additional customer payments.

During the year ended December 31, 2018, net revenue recognized from our performance obligations satisfied in previous periods was not material.

Disaggregation of Revenue


	Year Ended December 31,
Revenue by Service Provided	2018				2017				2016
HVAC and Plumbing	$	1,976,374	90.5	%	$	1,615,468	90.4	%	$	1,462,980	89.5	%
Building Automation Control Systems		95,093	4.4	%		94,041	5.3	%		90,461	5.5	%
Other		111,412	5.1	%		78,413	4.4	%		80,899	4.9	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

	Year Ended December 31,
Revenue by Type of Customer	2018				2017				2016
Industrial	$	596,557	27.3	%	$	395,362	22.1	%	$	378,499	23.2	%
Education		391,937	18.0	%		351,808	19.7	%		307,195	18.8	%
Office Buildings		288,090	13.2	%		248,604	13.9	%		202,187	12.4	%
Healthcare		319,958	14.7	%		224,643	12.6	%		197,797	12.1	%
Government		143,958	6.6	%		140,843	7.9	%		160,414	9.8	%
Retail, Restaurants and Entertainment		225,348	10.3	%		223,593	12.5	%		196,094	12.0	%
Multi-Family and Residential		136,075	6.2	%		116,844	6.5	%		122,766	7.5	%
Other		80,956	3.7	%		86,225	4.8	%		69,388	4.2	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

	Year Ended December 31,
Revenue by Activity Type	2018				2017				2016
New Construction	$	829,978	38.0	%	$	684,687	38.3	%	$	653,488	40.0	%
Existing Building Construction		796,946	36.5	%		580,737	32.4	%		514,437	31.5	%
Service Projects		206,506	9.5	%		197,703	11.1	%		178,455	10.9	%
Service Calls, Maintenance and Monitoring		349,448	16.0	%		324,795	18.2	%		287,960	17.6	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

Accounts Receivable

Contract Assets and Liabilities

The following table presents the changes in contract assets and contract liabilities (in thousands):


	Year Ended
	December 31, 2018
	Contract		Contract
	Assets		Liabilities
Balance at beginning of period	$	30,116	$	106,005
Change due to acquisitions		2,833		8,195
Change due to conditional versus unconditional		6,244		—
Reclassified to unbilled accounts receivable		(28,980)		—
Change in timing for performance obligation to be satisfied		—		16,786
Balance at December 31, 2018	$	10,213	$	130,986

During the years ended December 31, 2018 and 2017, we recognized revenue of $97.6 million and $86.6 million related to our contract liabilities at January 1, 2018 and January 1, 2017, respectively.

We did not have any impairment losses recognized on our receivables or contract assets in 2018 and 2017.

Remaining Performance Obligations

Accounts Receivable

Inventories

Property and Equipment

Recoverability of Goodwill and Identifiable Intangible Assets

We amortize identifiable intangible assets with finite lives over their useful lives. Changes in strategy and/or market condition may result in adjustments to recorded intangible asset balances.

Long-Lived Assets

Long‑Lived Assets

Acquisitions

We recognize assets acquired and liabilities assumed in business combinations, including contingent assets and liabilities, based on fair value estimates as of the date of acquisition.

Self-Insurance Liabilities

Self‑Insurance Liabilities

Warranty Costs

Income Taxes

Segment Disclosure

Concentrations of Credit Risk

Financial Instruments

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Schedule of cash paid

Cash paid (in thousands) for:


	Year Ended December 31,
	2018		2017		2016
Interest	$	3,743	$	2,832	$	1,864
Income taxes	$	33,401	$	38,144	$	29,349

Schedule of contracts in progress

Contracts in progress are as follows (in thousands):


	December 31,
	2018		2017
Costs incurred on contracts in progress	$	1,574,460	$	1,288,330
Estimated earnings, net of losses		300,514		253,641
Less—Billings to date		(1,958,567)		(1,617,860)
Less—Unbilled accounts receivable		(37,180)		—
	$	(120,773)	$	(75,889)

Costs and estimated earnings in excess of billings	$	10,213	$	30,116
Billings in excess of costs and estimated earnings		(130,986)		(106,005)
	$	(120,773)	$	(75,889)

Schedule of disaggregation or revenue

Our consolidated 2018 revenue was derived from the following service activities, all of which are in the mechanical services industry, the single industry segment we serve. See details in the following tables (dollars in thousands):


	Year Ended December 31,
Revenue by Service Provided	2018				2017				2016
HVAC and Plumbing	$	1,976,374	90.5	%	$	1,615,468	90.4	%	$	1,462,980	89.5	%
Building Automation Control Systems		95,093	4.4	%		94,041	5.3	%		90,461	5.5	%
Other		111,412	5.1	%		78,413	4.4	%		80,899	4.9	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

	Year Ended December 31,
Revenue by Type of Customer	2018				2017				2016
Industrial	$	596,557	27.3	%	$	395,362	22.1	%	$	378,499	23.2	%
Education		391,937	18.0	%		351,808	19.7	%		307,195	18.8	%
Office Buildings		288,090	13.2	%		248,604	13.9	%		202,187	12.4	%
Healthcare		319,958	14.7	%		224,643	12.6	%		197,797	12.1	%
Government		143,958	6.6	%		140,843	7.9	%		160,414	9.8	%
Retail, Restaurants and Entertainment		225,348	10.3	%		223,593	12.5	%		196,094	12.0	%
Multi-Family and Residential		136,075	6.2	%		116,844	6.5	%		122,766	7.5	%
Other		80,956	3.7	%		86,225	4.8	%		69,388	4.2	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

	Year Ended December 31,
Revenue by Activity Type	2018				2017				2016
New Construction	$	829,978	38.0	%	$	684,687	38.3	%	$	653,488	40.0	%
Existing Building Construction		796,946	36.5	%		580,737	32.4	%		514,437	31.5	%
Service Projects		206,506	9.5	%		197,703	11.1	%		178,455	10.9	%
Service Calls, Maintenance and Monitoring		349,448	16.0	%		324,795	18.2	%		287,960	17.6	%
Total	$	2,182,879	100.0	%	$	1,787,922	100.0	%	$	1,634,340	100.0	%

Schedule of contract assets and liabilities

The following table presents the changes in contract assets and contract liabilities (in thousands):


	Year Ended
	December 31, 2018
	Contract		Contract
	Assets		Liabilities
Balance at beginning of period	$	30,116	$	106,005
Change due to acquisitions		2,833		8,195
Change due to conditional versus unconditional		6,244		—
Reclassified to unbilled accounts receivable		(28,980)		—
Change in timing for performance obligation to be satisfied		—		16,786
Balance at December 31, 2018	$	10,213	$	130,986

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Measurements

Summary of fair values and levels within the fair value hierarchy in which the fair value measurements fall for assets and liabilities measured on a recurring basis


	Fair Value Measurements at December 31, 2018
	Level 1		Level 2		Level 3		Total
Cash and cash equivalents	$	45,620	$	—	$	—	$	45,620
Life insurance—cash surrender value	$	—	$	3,252	$	—	$	3,252
Contingent earn-out obligations	$	—	$	—	$	7,375	$	7,375

	Fair Value Measurements at December 31, 2017
	Level 1		Level 2		Level 3		Total
Cash and cash equivalents	$	36,542	$	—	$	—	$	36,542
Life insurance—cash surrender value	$	—	$	3,128	$	—	$	3,128
Contingent earn-out obligations	$	—	$	—	$	7,993	$	7,993

Schedule of reconciliation of the fair value of contingent earn-out obligations that use significant unobservable inputs (Level 3)

The table below presents a reconciliation of the fair value of our contingent earn‑out obligations that use significant unobservable inputs (Level 3) (in thousands).


	December 31,
	2018		2017
Balance at beginning of year	$	7,993	$	2,531
Issuances		4,366		11,755
Settlements		(7,050)		(2,578)
Adjustments to fair value		2,066		(3,715)
Balance at end of year	$	7,375	$	7,993

Goodwill and Identifiable Intangible Assets, Net (Tables)

12 Months Ended

Dec. 31, 2018

Goodwill and Identifiable Intangible Assets, Net

Schedule of changes in the carrying amount of goodwill

The changes in the carrying amount of goodwill are as follows (in thousands):


	December 31,
	2018		2017
Balance at beginning of year	$	200,584	$	149,208
Additions (See Note 4)		34,598		52,481
Impairment adjustment		—		(1,105)
Balance at end of year	$	235,182	$	200,584

Schedule of components of identifiable intangible assets

Identifiable intangible assets consist of the following (dollars in thousands):


		December 31,
	Estimated	2018				2017
	Useful Lives	Gross Book		Accumulated		Gross Book		Accumulated
	in Years	Value		Amortization		Value		Amortization
Customer relationships	1 - 15	$	128,480	$	(60,731)	$	98,244	$	(47,057)
Backlog	1 - 2		9,100		(8,260)		6,300		(5,478)
Tradenames	2 - 25		39,395		(12,709)		35,340		(11,305)
Total		$	176,975	$	(81,700)	$	139,884	$	(63,840)

Schedule of future amortization expense of identifiable intangible assets

At December 31, 2018, future amortization expense of identifiable intangible assets is as follows (in thousands):


Year ended December 31—
2019	$	18,088
2020		15,103
2021		12,060
2022		9,866
2023		8,478
Thereafter		31,680
Total	$	95,275

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2018

Property and Equipment

Schedule of components of property and equipment

Property and equipment consist of the following (dollars in thousands):


	Estimated
	Useful Lives	December 31,
	in Years	2018		2017
Land	—	$	5,702	$	2,745
Transportation equipment	1 - 7		98,898		87,120
Machinery and equipment	1 - 20		33,907		30,064
Computer and telephone equipment	1 - 10		20,179		20,463
Buildings and leasehold improvements	1 - 40		53,559		38,422
Furniture and fixtures	1 - 17		4,879		4,473
Construction in progress	—		1,715		12,614
			218,839		195,901
Less—Accumulated depreciation			(119,221)		(108,310)
Property and equipment, net		$	99,618	$	87,591

Detail of Certain Balance Sheet Accounts (Tables)

12 Months Ended

Dec. 31, 2018

Detail of Certain Balance Sheet Accounts

Schedule of activity in allowance for doubtful accounts

Activity in our allowance for doubtful accounts consists of the following (in thousands):


	December 31,
	2018		2017		2016
Balance at beginning of year	$	3,400	$	4,288	$	5,158
Bad debt expense (benefit)		3,562		182		(27)
Deductions for uncollectible receivables written off, net of recoveries		(1,304)		(1,829)		(876)
Allowance for doubtful accounts of acquired companies at date of acquisition		240		759		33
Balance at end of year	$	5,898	$	3,400	$	4,288

Schedule of other current liabilities

Other current liabilities consist of the following (in thousands):


	December 31,
	2018		2017
Accrued warranty costs	$	6,453	$	6,149
Accrued job losses		1,495		598
Accrued sales and use tax		2,685		2,308
Deferred revenue		5,233		3,895
Liabilities due to former owners		2,045		2,981
Other current liabilities		14,941		17,723
	$	32,852	$	33,654

Debt Obligations (Tables)

12 Months Ended

Dec. 31, 2018

Debt Obligations

Schedule of components of debt obligations

Debt obligations consist of the following (in thousands):


	December 31,
	2018		2017
Revolving credit facility	$	50,000	$	45,000
Notes to former owners		26,813		15,325
Other debt		105		214
Total debt		76,918		60,539
Less—current portion		(3,279)		(613)
Total long-term portion of debt	$	73,639	$	59,926

Schedule of future principal payments of long-term debt

At December 31, 2018, future principal payments of debt are as follows (in thousands):


Year ended December 31—
2019	$	3,279
2020		13,822
2021		9,817
2022		—
2023		50,000
	$	76,918

Schedule of interest expense

Interest expense included the following primary elements (in thousands):


	Year Ended December 31,
	2018		2017		2016
Interest expense on notes to former owners	$	642	$	365	$	70
Interest expense on borrowings and unused commitment fees		2,211		1,862		1,251
Letter of credit fees		474		553		657
Amortization of debt financing costs		383		376		367
Total	$	3,710	$	3,156	$	2,345

Schedule of reconciliation of Credit Facility Adjusted EBITDA to net income

The following is a reconciliation of Credit Facility Adjusted EBITDA to net income for 2018 (in thousands):


Net income	$	112,903
Provision for income taxes		35,773
Interest expense, net		3,637
Depreciation and amortization expense		42,689
Stock-based compensation		7,161
Pre-acquisition results of acquired companies, as defined under the Facility		3,771
Credit Facility Adjusted EBITDA	$	205,934

Schedule of market rates relating to interest options under the Facility

the following are the respective market rates as of December 31, 2018 relating to interest options under the Facility:


Base Rate Loan Option:
Federal Funds Rate plus 0.50%		2.95%
Wells Fargo Bank, N.A. Prime Rate		5.50%
One-month LIBOR plus 1.00%		3.52%
Eurodollar Rate Loan Option:
One-month LIBOR		2.52%
Six-month LIBOR		2.87%

Summary of additional margins


	Consolidated Total Indebtedness to
	Credit Facility Adjusted EBITDA
	Less than 1.00		1.00 to 1.75		1.75 to 2.50		2.50 or greater
Additional Per Annum Interest Margin Added Under:
Base Rate Loan Option	0.25	%	0.50	%	0.75	%	1.00	%
Eurodollar Rate Loan Option	1.25	%	1.50	%	1.75	%	2.00	%
Letter of credit fees	1.25	%	1.50	%	1.75	%	2.00	%
Commitment fees on any portion of the Revolving Loan capacity not in use for borrowings or letters of credit at any given time	0.20	%	0.25	%	0.30	%	0.35	%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Taxes

Schedule of provision for income taxes relating to continuing operations

Our provision for income taxes relating to continuing operations consists of the following (in thousands):


	December 31,
	2018		2017		2016
Current tax provision—
Federal	$	22,728	$	35,434	$	32,721
State and Puerto Rico		8,589		6,054		4,683
Total current		31,317		41,488		37,404
Deferred tax provision (benefit)—
Federal		4,347		5,391		(2,101)
State and Puerto Rico		109		(1,213)		862
Total deferred		4,456		4,178		(1,239)
Provision for income taxes	$	35,773	$	45,666	$	36,165

Schedule of difference in income taxes provided for and the amounts determined by applying the federal statutory tax rate to income before income taxes results


	December 31,
	2018			2017			2016
Federal statutory rate of—		21	%		35	%		35	%
Income taxes at the federal statutory rate	$	31,222		$	35,328		$	35,371
Increases (decreases) resulting from—
Net state income taxes		7,470			2,838			4,262
Valuation allowances		(2,852)			91			(1,254)
Net unrecognized tax benefits		(15)			153			20
Nondeductible expenses		1,926			1,134			825
R&D tax credits		(2,726)			—			—
Net operating loss carryforwards		2,225			—			—
Stock-based compensation deductions		(1,293)			(1,320)			(885)
Domestic production activities deduction		—			(2,112)			(2,026)
Corporate tax rate reduction to 21%		—			9,478			—
Other		(184)			76			(148)
Provision for income taxes	$	35,773		$	45,666		$	36,165

Schedule of significant components of the net deferred tax assets and net deferred tax liabilities as reflected on the balance sheet

Significant components of the deferred tax assets and deferred tax liabilities as reflected on the balance sheets are as follows (in thousands):


	Year Ended
	December 31,
	2018		2017
Deferred tax assets—
Accounts receivable and allowance for doubtful accounts	$	1,445	$	715
Stock-based compensation		2,538		2,297
Accrued liabilities and expenses		19,449		19,555
Net operating loss carryforwards		3,242		6,007
Intangible assets		5,071		2,272
Other		550		544
Subtotal		32,295		31,390
Valuation allowances		(648)		(3,500)
Total deferred tax assets		31,647		27,890
Deferred tax liabilities—
Property and equipment		(10,488)		(4,668)
Long-term contracts		(688)		(625)
Goodwill		(3,864)		(1,572)
Other		(360)		(322)
Total deferred tax liabilities		(15,400)		(7,187)
Net deferred tax assets	$	16,247	$	20,703

Schedule of deferred income tax assets and liabilities included in the consolidated balance sheets

The deferred tax assets and liabilities reflected above are included in the consolidated balance sheets as follows (in thousands):


	December 31,
	2018		2017
Deferred tax assets	$	17,634	$	22,966
Deferred tax liabilities	$	1,387	$	2,263

Schedule of reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding accrued interest and penalties

A reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding accrued interest and penalties, is as follows (in thousands):


	Year Ended
	December 31,
	2018		2017		2016
Balance at beginning of year	$	8,929	$	240	$	240
Additions based on tax positions related to current year		—		8,689		—
Additions based on tax positions related to prior years		2,726		—		—
Reductions for tax positions related to prior years		(8,689)		—		—
Reductions for settlements with tax authorities		—		—		—
Balance at end of year	$	2,966	$	8,929	$	240

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies

Schedule of future minimum rental payments under noncancelable operating leases

The following represents future minimum rental payments under noncancelable operating leases (in thousands):


Year ended December 31—
2019	$	13,503
2020		10,768
2021		9,449
2022		7,707
2023		6,402
Thereafter		28,328
	$	76,157

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2018

Stockholders' Equity

Reconciliation of number of shares outstanding with the number of shares used in computing basic and diluted earnings per share

The following table reconciles the number of shares outstanding with the number of shares used in computing basic and diluted earnings per share for each of the periods presented (in thousands):



	Year Ended December 31,
	2018	2017	2016
Common shares outstanding, end of period	36,894	37,187	37,209
Effect of using weighted average common shares outstanding	308	52	126
Shares used in computing earnings per share—basic	37,202	37,239	37,335
Effect of shares issuable under stock option plans based on the treasury stock method	283	316	330
Effect of restricted and contingently issuable shares	107	117	146
Shares used in computing earnings per share—diluted	37,592	37,672	37,811

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Stock-Based Compensation

Summary of activity under the entity's stock option plans

The following table summarizes activity under our stock option plans (shares in thousands):


	Year Ended
	December 31,
	2018
		Weighted-
		Average
Stock Options	Shares	Exercise Price
Outstanding at beginning of year	630	$	20.03
Granted	87	$	42.50
Exercised	(207)	$	15.01
Forfeited	(11)	$	38.08
Expired	—	$	—
Outstanding at end of year	499	$	25.65
Options exercisable at end of year	336

Summary information about stock options outstanding

The following table summarizes information about stock options outstanding at December 31, 2018 (shares in thousands):


	Options Outstanding				Options Exercisable
		Weighted-
		Average
	Number	Remaining	Weighted-		Number	Weighted-
	Outstanding at	Contractual	Average		Exercisable at	Average
Range of Exercise Prices	12/31/2018	Life	Exercise Price		12/31/2018	Exercise Price
$11.00 - $15.00	109	3.54	$	13.61	109	$	13.61
$15.01 - $20.00	158	5.70	$	17.83	158	$	17.83
$20.01 - $36.25	232	8.24	$	36.58	69	$	32.38
$11.00 - $36.25	499	6.41	$	25.65	336	$	19.46

Schedule of fair values and the assumptions used for the grants


	Year Ended December 31,
	2018		2017		2016
Weighted-average fair value per share of options granted	$	13.06	$	11.43	$	9.94
Fair value assumptions:
Expected dividend yield		0.79%		0.89%		0.97%
Expected stock price volatility		31.7%		34.5%		37.9%
Risk-free interest rate		2.66%		2.11%		1.41%
Expected term		5.3 years		5.3 years		5.3 years

Summary of information about nonvested stock option awards and changes

The following table summarizes information about nonvested stock option awards as of December 31, 2018 and changes for the year ended December 31, 2018 (shares in thousands):


		Weighted-Average
		Grant Date
Stock Options	Shares	Fair Value
Nonvested at December 31, 2017	186	$	9.85
Granted	87	$	13.06
Vested	(99)	$	8.91
Forfeited	(11)	$	11.92
Nonvested at December 31, 2018	163	$	11.99

Summary of activity under the entity's restricted stock plans

The following table summarizes activity under our restricted stock plans (shares in thousands):


	Year Ended
	December 31,
	2018
		Weighted
		Average Grant
Restricted Stock and Restricted Stock Units	Shares	Date Fair Value
Unvested at beginning of year	92	$	30.48
Granted	69	$	44.02
Vested	(77)	$	34.17
Forfeited	(6)	$	40.01
Unvested at end of year	78	$	38.17

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Selected Quarterly Financial Data (Unaudited)

Schedule of quarterly financial information

Quarterly financial information for the years ended December 31, 2018 and 2017 is summarized as follows (in thousands, except per share data):


	2018
	Q1		Q2		Q3		Q4
Revenue	$	464,941	$	535,043	$	594,536	$	588,359
Gross profit		89,053		111,183		127,868		118,175
Net income		16,659		32,547		38,541		25,156
INCOME PER SHARE:
Basic	$	0.45	$	0.87	$	1.03	$	0.68
Diluted	$	0.44	$	0.87	$	1.02	$	0.67


	2017
	Q1		Q2		Q3		Q4
Revenue	$	380,588	$	465,411	$	480,851	$	461,072
Gross profit		75,954		95,738		100,858		93,731
Net income (1)		7,477		17,972		22,284		7,539
INCOME PER SHARE:
Basic	$	0.20	$	0.48	$	0.60	$	0.20
Diluted	$	0.20	$	0.48	$	0.59	$	0.20

In the fourth quarter of 2017, we recorded a $9.5 million increase to the provision for income taxes to remeasure our net deferred tax assets for the enacted corporate tax rate reduction.

Business and Organization (Details)	12 Months Ended
Business and Organization (Details)	Dec. 31, 2018
Installation of systems in newly constructed facilities
Business and Organization
Percentage of revenue attributable to services	38.00%
Maintenance, repair and replacement services
Business and Organization
Percentage of revenue attributable to services	62.00%

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
Cash paid for:
Interest	$ 3,743	$ 2,832	$ 1,864
Income taxes	33,401	38,144	$ 29,349
Contracts in progress
Costs incurred on contracts in progress	1,574,460	1,288,330
Estimated earnings, net of losses	300,514	253,641
Less—Billings to date	(1,958,567)	(1,617,860)
Less—Unbilled accounts receivable	(37,180)
Contracts in progress	(120,773)	(75,889)
Costs and estimated earnings in excess of billings	10,213	30,116
Billings in excess of costs and estimated earnings	$ (130,986)	(106,005)
Period during which progress billings or contract price can be withheld until completion of work	6 months
Retention receivable	$ 80,800	68,700
Retention payable	$ 13,700	$ 11,900
ASU 2016-02
Recent Accounting Pronouncements
Operating lease, right-of-use assets				$ 75,000
Operating lease liability				$ 75,000

Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue
Revenue, Performance Obligation, Description of Payment Terms	We typically invoice our customers with payment terms of net due in 30 days
Receivable payment terms (in days)	30 days
Revenue	$ 2,182,879
Percentage of revenue from contract with customer (as a percent)	100.00%
Industrial
Disaggregation of Revenue
Revenue	$ 596,557
Percentage of revenue from contract with customer (as a percent)	27.30%
Education
Disaggregation of Revenue
Revenue	$ 391,937
Percentage of revenue from contract with customer (as a percent)	18.00%
Office Buildings
Disaggregation of Revenue
Revenue	$ 288,090
Percentage of revenue from contract with customer (as a percent)	13.20%
Healthcare
Disaggregation of Revenue
Revenue	$ 319,958
Percentage of revenue from contract with customer (as a percent)	14.70%
Government
Disaggregation of Revenue
Revenue	$ 143,958
Percentage of revenue from contract with customer (as a percent)	6.60%
Retail, Restaurants and Entertainment
Disaggregation of Revenue
Revenue	$ 225,348
Percentage of revenue from contract with customer (as a percent)	10.30%
Multi-Family and Residential
Disaggregation of Revenue
Revenue	$ 136,075
Percentage of revenue from contract with customer (as a percent)	6.20%
Other
Disaggregation of Revenue
Revenue	$ 80,956
Percentage of revenue from contract with customer (as a percent)	3.70%
New Construction
Disaggregation of Revenue
Revenue	$ 829,978
Percentage of revenue from contract with customer (as a percent)	38.00%
Existing Building Construction
Disaggregation of Revenue
Revenue	$ 796,946
Percentage of revenue from contract with customer (as a percent)	36.50%
Service Projects
Disaggregation of Revenue
Revenue	$ 206,506
Percentage of revenue from contract with customer (as a percent)	9.50%
Service Calls, Maintenance and Monitoring
Disaggregation of Revenue
Revenue	$ 349,448
Percentage of revenue from contract with customer (as a percent)	16.00%
HVAC and Plumbing
Disaggregation of Revenue
Revenue	$ 1,976,374
Percentage of revenue from contract with customer (as a percent)	90.50%
Building Automation Control Systems
Disaggregation of Revenue
Revenue	$ 95,093
Percentage of revenue from contract with customer (as a percent)	4.40%
Other
Disaggregation of Revenue
Revenue	$ 111,412
Percentage of revenue from contract with customer (as a percent)	5.10%
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue
Revenue		$ 1,787,922	$ 1,634,340
Percentage of revenue from contract with customer (as a percent)		100.00%	100.00%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Industrial
Disaggregation of Revenue
Revenue		$ 395,362	$ 378,499
Percentage of revenue from contract with customer (as a percent)		22.10%	23.20%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Education
Disaggregation of Revenue
Revenue		$ 351,808	$ 307,195
Percentage of revenue from contract with customer (as a percent)		19.70%	18.80%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Office Buildings
Disaggregation of Revenue
Revenue		$ 248,604	$ 202,187
Percentage of revenue from contract with customer (as a percent)		13.90%	12.40%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Healthcare
Disaggregation of Revenue
Revenue		$ 224,643	$ 197,797
Percentage of revenue from contract with customer (as a percent)		12.60%	12.10%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Government
Disaggregation of Revenue
Revenue		$ 140,843	$ 160,414
Percentage of revenue from contract with customer (as a percent)		7.90%	9.80%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Retail, Restaurants and Entertainment
Disaggregation of Revenue
Revenue		$ 223,593	$ 196,094
Percentage of revenue from contract with customer (as a percent)		12.50%	12.00%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Multi-Family and Residential
Disaggregation of Revenue
Revenue		$ 116,844	$ 122,766
Percentage of revenue from contract with customer (as a percent)		6.50%	7.50%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Other
Disaggregation of Revenue
Revenue		$ 86,225	$ 69,388
Percentage of revenue from contract with customer (as a percent)		4.80%	4.20%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| New Construction
Disaggregation of Revenue
Revenue		$ 684,687	$ 653,488
Percentage of revenue from contract with customer (as a percent)		38.30%	40.00%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Existing Building Construction
Disaggregation of Revenue
Revenue		$ 580,737	$ 514,437
Percentage of revenue from contract with customer (as a percent)		32.40%	31.50%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Service Projects
Disaggregation of Revenue
Revenue		$ 197,703	$ 178,455
Percentage of revenue from contract with customer (as a percent)		11.10%	10.90%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Service Calls, Maintenance and Monitoring
Disaggregation of Revenue
Revenue		$ 324,795	$ 287,960
Percentage of revenue from contract with customer (as a percent)		18.20%	17.60%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| HVAC and Plumbing
Disaggregation of Revenue
Revenue		$ 1,615,468	$ 1,462,980
Percentage of revenue from contract with customer (as a percent)		90.40%	89.50%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Building Automation Control Systems
Disaggregation of Revenue
Revenue		$ 94,041	$ 90,461
Percentage of revenue from contract with customer (as a percent)		5.30%	5.50%
Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Other
Disaggregation of Revenue
Revenue		$ 78,413	$ 80,899
Percentage of revenue from contract with customer (as a percent)		4.40%	4.90%
Minimum
Disaggregation of Revenue
Payments received term (in days)	30 days
Maximum
Disaggregation of Revenue
Payments received term (in days)	90 days

Summary of Significant Accounting Policies - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Contract Assets
Balance at beginning of period	$ 30,116
Change due to acquisitions	2,833
Change due to conditional versus unconditional	6,244
Reclassified to unbilled accounts receivable	(28,980)
Balance at end of period	10,213	$ 30,116
Contract Liabilities
Balance at beginning of period	106,005
Change due to acquisitions	8,195
Change in timing for performance obligation to be satisfied	16,786
Balance at end of period	130,986	106,005
Revenue related to our contract liabilities	$ 97,600
The term of the renewable service maintenance agreements (in years)	1 year
Practical Expedient	true
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Contract Liabilities
Revenue related to our contract liabilities		$ 86,600

Summary of Significant Accounting Policies - Remaining Performance Obligations (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01 $ in Millions	Dec. 31, 2018 USD ($)
Remaining Performance Obligations
Remaining performance obligations	$ 1,170
Expected percentage of remaining performance obligations	85.00%
Expected timing of performance obligations	12 months

Summary of Significant Accounting Policies - Risk (Details)	12 Months Ended
	Dec. 31, 2018 item
Warranty Costs
Labor warranty period after servicing of existing HVAC system	30 days
Revenue \| Customer concentration
Warranty Costs
Number of single customers accounting for more than threshold concentration risk percentage	0
Revenue \| Customer concentration \| Minimum
Warranty Costs
Single customer, percentage of revenue	4.00%

Fair Value Measurements (Details) $ in Thousands	3 Months Ended	12 Months Ended
Fair Value Measurements (Details) $ in Thousands	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)
Fair Value Measurements
Number of employees covered under life insurance policies \| item		58
Combined face value of life insurance policies		$ 42,000
Cash surrender value		3,300	$ 3,100
Reconciliation of the fair value of contingent earn-out obligations that use significant unobservable inputs (Level 3)
Goodwill impairment	$ 1,100		1,105
Contingent earn-out obligations
Reconciliation of the fair value of contingent earn-out obligations that use significant unobservable inputs (Level 3)
Balance at beginning of year	$ 2,531	7,993	2,531
Issuances		4,366	11,755
Settlements		(7,050)	(2,578)
Adjustments to fair value		(2,066)	3,715
Balance at end of period		7,375	7,993
Recurring basis \| Total
Fair Value Measurements
Cash and cash equivalents		45,620	36,542
Life insurance—cash surrender value		3,252	3,128
Contingent earn-out obligations		7,375	7,993
Recurring basis \| Quoted Market Prices In Active Markets for Identical Assets (Level 1)
Fair Value Measurements
Cash and cash equivalents		45,620	36,542
Recurring basis \| Fair Value Measurements at Reporting Date Using Significant Other Observable Inputs (Level 2)
Fair Value Measurements
Life insurance—cash surrender value		3,252	3,128
Recurring basis \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Contingent earn-out obligations		7,375	7,993
Non recurring basis \| Significant Unobservable Inputs (Level 3)
Reconciliation of the fair value of contingent earn-out obligations that use significant unobservable inputs (Level 3)
Goodwill impairment		$ 0	$ 1,100

Acquisitions (Details)		3 Months Ended					12 Months Ended
Acquisitions (Details)	Jan. 01, 2016 USD ($)	Sep. 30, 2018 item	Jun. 30, 2018 item	Mar. 31, 2018 item	Jun. 30, 2017 USD ($)	Mar. 31, 2016 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) item
Acquisitions
Total purchase price							$ 95,600,000	$ 9,400,000
Number of acquisitions \| item		2	3	2		2		4
Number of acquisitions reported as separate operating location \| item		1
Environmental Air Systems
Acquisitions
Total purchase price	$ 46,600,000
Purchase price paid in cash	$ 42,000,000
Interest acquired (as a percent)	40.00%
Shoffner
Acquisitions
Total purchase price						$ 19,800,000
Amount allocated to goodwill and identifiable intangible assets for acquisitions						14,800,000
Purchase price paid in cash						$ 15,500,000
Interest acquired (as a percent)						100.00%
BCH
Acquisitions
Total purchase price					$ 121,300,000
Amount allocated to goodwill and identifiable intangible assets for acquisitions					97,000,000
Purchase price paid in cash					95,400,000
Promissory note payable					14,300,000
Contingent earn-out obligation					$ 11,600,000
Other Acquisitions
Acquisitions
Total purchase price						$ 100,000.00000
Number of acquisitions \| item						1

Goodwill and Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Balance at beginning of year	$ 149,208	$ 200,584	$ 149,208
Additions (See Note 4)		34,598	52,481
Impairment adjustment	$ (1,100)		(1,105)
Balance at end of period		$ 235,182	$ 200,584
Impairment testing, Scenario one
Impairment Testing
Impairment testing, discounted cash flow analysis weightage assigned		50.00%
Impairment testing, Scenario two
Impairment Testing
Impairment testing, public company approach weightage assigned		50.00%

Goodwill and Identifiable Intangible Assets, Net - Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Identifiable Intangible Assets, Net
Gross Book Value	$ 176,975	$ 139,884
Accumulated Amortization	(81,700)	(63,840)
Amortization of identifiable intangible assets	20,089	17,404	$ 8,185
Future amortization expense of identifiable intangible assets
2019	18,088
2020	15,103
2021	12,060
2022	9,866
2023	8,478
Thereafter	31,680
Total	95,275
Customer relationships
Identifiable Intangible Assets, Net
Gross Book Value	128,480	98,244
Accumulated Amortization	$ (60,731)	(47,057)
Customer relationships \| Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year
Customer relationships \| Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	15 years
Backlog
Identifiable Intangible Assets, Net
Gross Book Value	$ 9,100	6,300
Accumulated Amortization	$ (8,260)	(5,478)
Backlog \| Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year
Backlog \| Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Tradenames
Identifiable Intangible Assets, Net
Gross Book Value	$ 39,395	35,340
Accumulated Amortization	$ (12,709)	$ (11,305)
Tradenames \| Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	2 years
Tradenames \| Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	25 years
Customer Relationships Noncompete Agreements and Tradenames \| Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year
Customer Relationships Noncompete Agreements and Tradenames \| Maximum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	25 years

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and equipment
Property and equipment, gross	$ 218,839	$ 195,901
Less—Accumulated depreciation	(119,221)	(108,310)
Property and equipment, net	99,618	87,591
Depreciation expense	22,600	20,100	$ 18,000
Land
Property and equipment
Property and equipment, gross	5,702	2,745
Transportation equipment
Property and equipment
Property and equipment, gross	$ 98,898	87,120
Transportation equipment \| Minimum
Property and equipment
Estimated useful life	1 year
Transportation equipment \| Maximum
Property and equipment
Estimated useful life	7 years
Machinery and equipment
Property and equipment
Property and equipment, gross	$ 33,907	30,064
Machinery and equipment \| Minimum
Property and equipment
Estimated useful life	1 year
Machinery and equipment \| Maximum
Property and equipment
Estimated useful life	20 years
Computer and telephone equipment
Property and equipment
Property and equipment, gross	$ 20,179	20,463
Computer and telephone equipment \| Minimum
Property and equipment
Estimated useful life	1 year
Computer and telephone equipment \| Maximum
Property and equipment
Estimated useful life	10 years
Buildings and leasehold improvements
Property and equipment
Property and equipment, gross	$ 53,559	38,422
Buildings and leasehold improvements \| Minimum
Property and equipment
Estimated useful life	1 year
Buildings and leasehold improvements \| Maximum
Property and equipment
Estimated useful life	40 years
Furniture and fixtures
Property and equipment
Property and equipment, gross	$ 4,879	4,473
Furniture and fixtures \| Minimum
Property and equipment
Estimated useful life	1 year
Furniture and fixtures \| Maximum
Property and equipment
Estimated useful life	17 years
Construction in progress
Property and equipment
Property and equipment, gross	$ 1,715	$ 12,614

Detail of Certain Balance Sheet Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Activity in allowance for doubtful accounts
Balance at beginning of year	$ 3,400	$ 4,288	$ 5,158
Bad debt expense (benefit)	3,562	182	(27)
Deductions for uncollectible receivables written off, net of recoveries	(1,304)	(1,829)	(876)
Allowance for doubtful accounts of acquired companies at date of acquisition	240	759	33
Balance at end of year	5,898	3,400	$ 4,288
Other current liabilities
Accrued warranty costs	6,453	6,149
Accrued job losses	1,495	598
Accrued sales and use tax	2,685	2,308
Deferred revenue	5,233	3,895
Liabilities due to former owners	2,045	2,981
Other current liabilities	14,941	17,723
Total other current liabilities	$ 32,852	$ 33,654

Debt Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Obligations
Total debt	$ 76,918	$ 60,539
Less—current portion	(3,279)	(613)
Total long-term portion of debt	73,639	59,926
Revolving credit facility
Debt Obligations
Total debt	50,000	45,000
Notes to former owners
Debt Obligations
Outstanding balance	26,813	15,325
Other debt
Debt Obligations
Total debt	$ 105	$ 214

Debt Obligations - Future Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Future principal payments of long-term debt
2019	$ 3,279
2020	13,822
2021	9,817
2023	50,000
Total debt	76,918
Interest expense
Interest expense on notes to former owners	642	$ 365	$ 70
Interest expense on borrowings and unused commitment fees	2,211	1,862	1,251
Letter of credit fees	474	553	657
Amortization of debt financing costs	383	376	367
Total	$ 3,710	$ 3,156	$ 2,345

Debt Obligations - Other (Details) $ in Thousands	12 Months Ended
Debt Obligations - Other (Details) $ in Thousands	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Apr. 30, 2018 USD ($)	Apr. 18, 2018 USD ($)	Apr. 17, 2018 USD ($)	Mar. 31, 2018 USD ($)
Reconciliation of Earnings before Interest Tax Depreciation and Amortization to Net Income
Net income	$ 112,903	$ 55,272	$ 64,896
Provision for income taxes	35,773	45,666	36,165
Stock-based compensation	7,161	6,377	$ 5,041
Other disclosures
Outstanding balance	73,639	59,926
Shoffner
Other disclosures
Outstanding balance	100
Acquired debt	$ 400
London Interbank Offered Rate (LIBOR) \| Shoffner
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	2.25%
Revolving credit facility
Debt Obligations
Outstanding borrowings	$ 50,000
Letters of credit amount outstanding	33,600
Credit available	316,400
Book value of assets pledged as collateral	$ 48,900
Number of quarters of net earnings used for the calculation of the credit facility adjusted EBITDA \| item	4
Reconciliation of Earnings before Interest Tax Depreciation and Amortization to Net Income
Net income	$ 112,903
Provision for income taxes	35,773
Interest expense, net	(3,637)
Depreciation and amortization expense	42,689
Stock-based compensation	7,161
Pre-acquisition results of acquired companies, as defined under the Facility	(3,771)
Credit Facility Adjusted EBITDA	$ 205,934
Principal financial covenants
Number of interest rate options \| item	2
Leverage ratio	0.40
Fixed charge coverage ratio	21.9
Number of quarters of capital expenditures, tax provision, dividends and stock repurchase payments used for calculation of fixed charge coverage ratio \| item	4
Period of Credit Facility Adjusted EBITDA for determining additional margins	12 months
Additional per annum interest margin added under:
Weighted average interest rate (as a percent)	3.70%
Revolving credit facility \| Through maturity
Principal financial covenants
Leverage ratio	3.00
Revolving credit facility \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Additional per annum interest margin added under:
Letter of credit fees (as a percent)	1.25%
Commitment fees payable on unused portion of the facility (as a percent)	0.20%
Revolving credit facility \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.00 to 1.75
Additional per annum interest margin added under:
Letter of credit fees (as a percent)	1.50%
Commitment fees payable on unused portion of the facility (as a percent)	0.25%
Revolving credit facility \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.75 to 2.50
Additional per annum interest margin added under:
Letter of credit fees (as a percent)	1.75%
Commitment fees payable on unused portion of the facility (as a percent)	0.30%
Revolving credit facility \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater
Additional per annum interest margin added under:
Letter of credit fees (as a percent)	2.00%
Commitment fees payable on unused portion of the facility (as a percent)	0.35%
Revolving credit facility \| Minimum
Principal financial covenants
Fixed charge coverage ratio	2.00
Revolving credit facility \| Minimum \| Covenant Requirement
Principal financial covenants
Net leverage ratio used as basis for other restrictions	2.00
Revolving credit facility \| Maximum
Principal financial covenants
Net leverage ratio after giving effect to stock repurchases for calculation of the fixed charge coverage ratio	1.75
Permitted amount of acquisitions per transaction	$ 40,000
Aggregate purchase price of current acquisition and acquisitions in the preceding 12 month period for determining permitted amount of acquisition per transaction	$ 80,000
Revolving credit facility \| Maximum \| Covenant Requirement
Principal financial covenants
Net leverage ratio used to determine exclusion of stock repurchases and the payment of dividends for calculation of the fixed charge coverage ratio	1.75
Revolving credit facility \| Maximum \| Stock Repurchases Through September 30, 2015
Principal financial covenants
Amount of stock repurchases to maintain maximum net leverage ratio	$ 30,000
Revolving credit facility \| Base Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	0.25%
Revolving credit facility \| Base Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.00 to 1.75
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	0.50%
Revolving credit facility \| Base Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.75 to 2.50
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	0.75%
Revolving credit facility \| Base Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	1.00%
Revolving credit facility \| Eurodollar Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	1.25%
Revolving credit facility \| Eurodollar Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.00 to 1.75
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	1.50%
Revolving credit facility \| Eurodollar Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.75 to 2.50
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	1.75%
Revolving credit facility \| Eurodollar Rate \| Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	2.00%
Amended senior revolving credit facility
Debt Obligations
Borrowing capacity					$ 400,000	$ 325,000
Line of credit borrowing capacity accordion option	$ 100,000
Financing and professional cost				$ 800
Unamortized costs							$ 1,100
Notes to former owners
Other disclosures
Cumulative number of companies acquired \| item	6
Outstanding balance	$ 26,813	$ 15,325
Subordinate note \| Shoffner
Other disclosures
Outstanding balance	$ 500
Weighted average interest rate (as a percent)	3.00%
Subordinate note \| Acquisition First Quarter 2018 [Member]
Other disclosures
Outstanding balance	$ 1,000
Weighted average interest rate (as a percent)	2.50%
Subordinate note \| Acquisition Second Quarter 2018 [Member]
Other disclosures
Outstanding balance	$ 1,000
Weighted average interest rate (as a percent)	3.50%
Promissory note \| BCH
Other disclosures
Outstanding balance	$ 14,300
Weighted average interest rate (as a percent)	3.00%
Promissory note \| Acquisition Third Quarter 2018 [Member]
Other disclosures
Outstanding balance	$ 6,500
Weighted average interest rate (as a percent)	3.50%
Promissory note \| Acquisition Two Third Quarter 2018 [Member]
Other disclosures
Outstanding balance	$ 3,500
Weighted average interest rate (as a percent)	2.90%
Federal Funds Rate \| Revolving credit facility \| Base Rate
Market rates relating to interest options
Market rate (as a percent)	2.95%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	0.50%
Wells Fargo Bank, N.A. Prime Rate \| Revolving credit facility \| Base Rate
Market rates relating to interest options
Market rate (as a percent)	5.50%
One-month LIBOR \| Revolving credit facility \| Base Rate
Market rates relating to interest options
Market rate (as a percent)	3.52%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)	1.00%
One-month LIBOR \| Revolving credit facility \| Eurodollar Rate
Market rates relating to interest options
Variable rate basis	One-month LIBOR
Market rate (as a percent)	2.52%
Six-month LIBOR \| Revolving credit facility \| Eurodollar Rate
Market rates relating to interest options
Variable rate basis	Six-month LIBOR
Market rate (as a percent)	2.87%

Income Taxes - Provision (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes - Provision (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current tax provision—
Federal	$ 22,728	$ 35,434	$ 32,721
State and Puerto Rico	8,589	6,054	4,683
Total current	31,317	41,488	37,404
Deferred tax provision (benefit)—
Federal	4,347	5,391	(2,101)
State and Puerto Rico	109	(1,213)	862
Total deferred	4,456	4,178	(1,239)
Provision for income taxes	$ 35,773	$ 45,666	$ 36,165

Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Effective tax rates on continuing operations			24.10%	45.20%	35.80%
Federal statutory income tax rate (as a percent)	21.00%		21.00%	35.00%	35.00%
Income taxes at the federal statutory rate of 35%			$ 31,222	$ 35,328	$ 35,371
Increases (decreases) resulting from—
Net state income taxes			7,470	2,838	4,262
Valuation allowances			(2,852)	91	(1,254)
Net unrecognized tax benefits			(15)	153	20
Nondeductible expenses			1,926	1,134	825
R&D tax credits			(2,726)
Net operating loss carryforwards			2,225
Stock-based compensation deductions			(1,293)	(1,320)	(885)
Domestic production activities deduction				(2,112)	(2,026)
Corporate tax rate reduction to 21%				9,478
Other			(184)	76	(148)
Provision for income taxes			$ 35,773	45,666	$ 36,165
Increase to provision for income taxes		$ 9,500		$ 9,500

Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets—
Accounts receivable and allowance for doubtful accounts	$ 1,445	$ 715
Stock-based compensation	2,538	2,297
Accrued liabilities and expenses	19,449	19,555
Net operating loss carryforwards	3,242	6,007
Intangible assets	5,071	2,272
Other	550	544
Subtotal	32,295	31,390
Valuation allowances	(648)	(3,500)
Total deferred tax assets	31,647	27,890
Deferred tax liabilities—
Property and equipment	(10,488)	(4,668)
Long-term contracts	(688)	(625)
Goodwill	(3,864)	(1,572)
Other	(360)	(322)
Total deferred tax liabilities	(15,400)	(7,187)
Net deferred tax assets	16,247	20,703
Deferred income tax assets
Deferred income tax assets	17,634	22,966
Deferred income tax liabilities
Deferred tax liabilities	$ 1,387	$ 2,263

Income Taxes - Loss Carryforwards and Other (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating loss carryforwards
Net deferred tax assets	$ 31,647	$ 27,890
Reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding accrued interest and penalties
Balance at beginning of year	8,929	240	$ 240
Additions based on tax positions related to current year		8,689
Additions based on tax positions related to prior years	2,726
Reductions for tax positions related to prior years	(8,689)
Reductions for settlements with tax authorities
Balance at end of year	2,966	8,929	240
Interest and penalties accrued	600	$ 700	$ 400
State
Operating loss carryforwards
Future tax benefits	3,200
Net operating loss carryforwards	55,500
Increase in valuation allowance	600
Net deferred tax assets	2,600
Maximum
Reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding accrued interest and penalties
Decrease in unrecognized tax benefits	$ 3,000

Employee Benefit Plans (Details) $ in Thousands	12 Months Ended
Employee Benefit Plans (Details) $ in Thousands	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Employee Benefit Plans
Percentage of contributions of covered employees' salaries or wages	2.50%
Contribution	$ 10,800	$ 7,800	$ 7,800
Amount payable to plan	$ 200	$ 500
Number of employees who are union members \| item	6	6
Contributions made to multi-employer pension plans	$ 0	$ 0	$ 0
Period in which certain individuals are entitled to fixed annual payments	15 years
Maximum age under which certain individuals are entitled to fixed annual payments	65 years
Portion of benefits vesting after ten years of completed service (as a percent)	50.00%
Period of completed service over which 50% of benefits are vested	10 years
Portion of benefits vesting after fifteen years of completed service (as a percent)	75.00%
Period of completed service over which 75% of benefits are vested	15 years
Period of service over which benefits are fully vested	20 years
Unfunded benefit liability	$ 4,300	$ 4,000

Commitments and Contingencies - Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Leases
Rent expense	$ 23,400	$ 21,100	$ 20,600
Future minimum rental payments under noncancelable operating leases
2019	13,503
2020	10,768
2021	9,449
2022	7,707
2023	6,402
Thereafter	28,328
Total future minimum rental payments	$ 76,157
Lease buildings \| Minimum
Leases
Lease term	3 years
Lease buildings \| Maximum
Leases
Lease term	10 years
Lease buildings \| Previous owners
Leases
Rent expense	$ 4,800	$ 4,800	$ 5,100

Commitments and Contingencies - Other and Bonds (Details) $ in Millions	1 Months Ended	3 Months Ended			12 Months Ended
	Apr. 30, 2018 claim	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) claim	Dec. 31, 2016 USD ($)	Dec. 31, 2018
Commitments and Contingencies
Gain on the claim settlement		$ 4.0
British Petroleum
Commitments and Contingencies
Number of claims settled \| claim	2		2
Gain on the claim settlement			$ 1.0	$ 0.6
Surety \| Minimum
Surety
Percentage of business which has required bonds					20.00%
Surety \| Maximum
Surety
Percentage of business which has required bonds					30.00%

Commitments and Contingencies - Self-Insurance (Details)	Dec. 31, 2018 USD ($) item
Workers' Compensation
Self-Insurance
Per incident deductible amount	$ 1,000,000
Amount of loss fully insured above per-incident deductible amount	1,000,000
Employer's Liability
Self-Insurance
Per incident deductible amount	1,000,000
Employer's Liability \| Maximum
Self-Insurance
Amount of excess loss insurance covered	100,000,000
General Liability
Self-Insurance
Per incident deductible amount	1,000,000
Amount of loss fully insured above per-incident deductible amount	1,000,000
General Liability \| Maximum
Self-Insurance
Amount of excess loss insurance covered	100,000,000
Auto Liability
Self-Insurance
Per incident deductible amount	500,000
Amount of loss fully insured above per-incident deductible amount	1,500,000
Auto Liability \| Maximum
Self-Insurance
Amount of excess loss insurance covered	$ 100,000,000
Employee Medical
Self-Insurance
Number of medical plans \| item	3
Employee Medical - Plan One
Self-Insurance
Per person, per policy deductible amount	$ 350,000
Employee Medical - Plan Two
Self-Insurance
Per person, per policy deductible amount	350,000
Employee Medical - Plan Three
Self-Insurance
Per incident deductible amount	$ 350,000

Stockholders' Equity - Incentive and Other (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	12 Months Ended			144 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	May 31, 2017	May 31, 2012	Mar. 29, 2007
Share Repurchase Program
Number of shares of outstanding common stock authorized to be acquired under a stock repurchase program	8.8			8.8			1.0
Share repurchase (in shares)				8.2
Average price (in dollars per share)	$ 48.13			$ 16.24
Share repurchase	$ 28,533	$ 9,007	$ 13,088
Repurchased carrying basis	$ 28,500			$ 28,500
Maximum
Share Repurchase Program
Share repurchase (in shares)	0.6
2012 Equity Incentive Plan
Stockholders' Equity
Number of shares authorized and reserved for issuance						5.1
Number of shares available for issuance	2.9			2.9
2017 Omnibus Incentive Plan
Stockholders' Equity
Number of shares authorized and reserved for issuance					2.9
Number of shares available for issuance	2.6			2.6

Stockholders' Equity - Anti-dilutive Stock options (Details) - Stock Options - shares shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share
Anti-dilutive securities excluded from computation of earnings per share amount (in shares)			0.1
Maximum
Earnings Per Share
Anti-dilutive securities excluded from computation of earnings per share amount (in shares)	0.1	0.1

Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the number of shares outstanding with the number of shares used in computing basic and diluted earnings per share
Common shares outstanding, end of period	36,894	37,187	37,209
Effect of using weighted average common shares outstanding	308	52	126
Shares used in computing earnings per share—basic	37,202	37,239	37,335
Effect of shares issuable under stock option plans based on the treasury stock method	283	316	330
Effect of restricted and contingently issuable shares	107	117	146
Shares used in computing earnings per share—diluted	37,592	37,672	37,811

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-Based Compensation
Stock-based compensation expense	$ 7.2	$ 6.4	$ 5.0
Income tax benefit	$ 1.5	$ 2.4	1.9
Minimum
Stock-Based Compensation
Sum of age and years of service for accelerated vesting on retirement of certain stock options and restricted stock awards	75 years
Stock Options
Stock-Based Compensation
Vesting period	3 years
Shares
Outstanding at beginning of year (in shares)	630
Granted (in shares)	87
Exercised (in shares)	(207)
Forfeited (in shares)	(11)
Outstanding at end of year (in shares)	499	630
Options exercisable at end of year (in shares)	336
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 20.03
Granted (in dollars per share)	42.50
Exercised (in dollars per share)	15.01
Forfeited (in dollars per share)	38.08
Outstanding at end of year (in dollars per share)	$ 25.65	$ 20.03
Other information
Intrinsic value of options exercised	$ 6.7	$ 3.6	$ 1.9
Weighted-average remaining contractual term of options exercisable	5 years 4 months 24 days
Aggregate intrinsic value of options exercisable	$ 8.1
Number of options that are vested and expected to vest (in shares)	500
Weighted average exercise price of options that are vested and expected to vest (in dollars per share)	$ 25.65
Weighted-average remaining contractual term of options that are vested and expected to vest	6 years 4 months 24 days
Aggregate intrinsic value of options that are vested and expected to vest	$ 9.0

Stock-Based Compensation - Stock Option Plan Activity (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2018 $ / shares shares
$11.00 - $15.00
Stock-Based Compensation
Exercise price, low end of range (in dollars per share)	$ 11.00
Exercise price, high end of range (in dollars per share)	15.00
$15.01 - $20.00
Stock-Based Compensation
Exercise price, low end of range (in dollars per share)	15.01
Exercise price, high end of range (in dollars per share)	20.00
$20.01 - $36.25
Stock-Based Compensation
Exercise price, low end of range (in dollars per share)	20.01
Exercise price, high end of range (in dollars per share)	36.25
$11.00 - $36.25
Stock-Based Compensation
Exercise price, low end of range (in dollars per share)	11.00
Exercise price, high end of range (in dollars per share)	$ 36.25
Stock Options \| $11.00 - $15.00
Options Outstanding
Number of Shares \| shares	109
Weighted-Average Remaining Contractual Life	3 years 6 months 15 days
Weighted-Average Exercise Price (in dollars per share)	$ 13.61
Options Exercisable
Number of Shares \| shares	109
Weighted-Average Exercise Price (in dollars per share)	$ 13.61
Stock Options \| $15.01 - $20.00
Options Outstanding
Number of Shares \| shares	158
Weighted-Average Remaining Contractual Life	5 years 8 months 12 days
Weighted-Average Exercise Price (in dollars per share)	$ 17.83
Options Exercisable
Number of Shares \| shares	158
Weighted-Average Exercise Price (in dollars per share)	$ 17.83
Stock Options \| $20.01 - $36.25
Options Outstanding
Number of Shares \| shares	232
Weighted-Average Remaining Contractual Life	8 years 2 months 27 days
Weighted-Average Exercise Price (in dollars per share)	$ 36.58
Options Exercisable
Number of Shares \| shares	69
Weighted-Average Exercise Price (in dollars per share)	$ 32.38
Stock Options \| $11.00 - $36.25
Options Outstanding
Number of Shares \| shares	499
Weighted-Average Remaining Contractual Life	6 years 4 months 28 days
Weighted-Average Exercise Price (in dollars per share)	$ 25.65
Options Exercisable
Number of Shares \| shares	336
Weighted-Average Exercise Price (in dollars per share)	$ 19.46

Stock-Based Compensation - Fair Value Assumptions (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) item $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares
Fair value assumptions:
Expected term		5 years 3 months 18 days	5 years 3 months 18 days
Additional information
Allocated Share-based Compensation Expense \| $	$ 7.2	$ 6.4	$ 5.0
Stock Options
Stock-Based Compensation
Weighted-average fair value per share of options granted (in dollars per share)	$ 13.06	$ 11.43	$ 9.94
Fair value assumptions:
Expected dividend yield (as a percent)	0.79%	0.89%	0.97%
Expected stock price volatility (as a percent)	31.70%	34.50%	37.90%
Risk-free interest rate (as a percent)	2.66%	2.11%	1.41%
Expected term	5 years 3 months 18 days
Other information
Compensation expense yet to be recognized \| $	$ 0.2
Weighted-average period over which compensation cost will be recognized	1 year 7 months 6 days
Total fair value of options vested \| $	$ 0.9
Nonvested Options, Shares
Nonvested at beginning of year (in shares) \| shares	186
Granted (in shares) \| shares	87
Vested (in shares) \| shares	(99)
Forfeited (in shares) \| shares	(11)
Nonvested at end of year (in shares) \| shares	163	186
Nonvested Options, Weighted-Average Grant Date Fair Value
Nonvested at beginning of year (in dollars per share)	$ 9.85
Granted (in dollars per share)	13.06	$ 11.43	$ 9.94
Vested (in dollars per share)	8.91
Forfeited (in dollars per share)	11.92
Nonvested at end of year (in dollars per share)	$ 11.99	$ 9.85
Additional information
Vesting period	3 years
Restricted Stock and Restricted Stock Units
Other information
Compensation expense yet to be recognized \| $	$ 0.7
Weighted-average period over which compensation cost will be recognized	1 year 8 months 12 days
Shares
Unvested at beginning of year (in shares) \| shares	92
Granted (in shares) \| shares	69
Vested (in shares) \| shares	(77)
Forfeited (in shares) \| shares	(6)
Unvested at end of year (in shares) \| shares	78	92
Weighted Average Grant Date Fair Value
Unvested at beginning of year (in dollars per share)	$ 30.48
Granted (in dollars per share)	44.02	$ 35.69	30.25
Vested (in dollars per share)	34.17
Forfeited (in dollars per share)	40.01
Unvested at end of year (in dollars per share)	$ 38.17	30.48
Additional information
Fair value of shares vested \| $	$ 2.6
Weighted-average fair value (in dollars per share)	$ 44.02	$ 35.69	$ 30.25
Aggregate intrinsic value of restricted stock vested \| $	$ 3.3	$ 3.2	$ 3.6
Performance Stock Units
Other information
Compensation expense yet to be recognized \| $	$ 0.4
Weighted-average period over which compensation cost will be recognized	1 year 2 months 12 days
Additional information
Vesting period	3 years
Types of performance units \| item	2
Percentage of units measured on stock price relative to peer group	50.00%
Percentage of units measured on stock price based on pre determined EPS	50.00%
Period for which shareholder return is compared with peer group for units determined by EPS performance	3 years
Calculated fair market value \| $	$ 5.3
Value of PSUs granted \| $	2.1
Allocated Share-based Compensation Expense \| $	$ 2.9	$ 2.6	$ 1.6
Performance Stock Units \| Minimum
Additional information
Performance measures for dollar denominated award granted	0
Performance Stock Units \| Maximum
Additional information
Performance measures for dollar denominated award granted	2.0

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Data (Unaudited)
Revenue	$ 588,359	$ 594,536	$ 535,043	$ 464,941	$ 461,072	$ 480,851	$ 465,411	$ 380,588	$ 2,182,879	$ 1,787,922	$ 1,634,340
Gross Profit	118,175	127,868	111,183	89,053	93,731	100,858	95,738	75,954	446,279	366,281	344,009
Net income	$ 25,156	$ 38,541	$ 32,547	$ 16,659	$ 7,539	$ 22,284	$ 17,972	$ 7,477	$ 112,903	$ 55,272	$ 64,896
Basic-
Basic (in dollars per share)	$ 0.68	$ 1.03	$ 0.87	$ 0.45	$ 0.20	$ 0.60	$ 0.48	$ 0.20	$ 3.03	$ 1.48	$ 1.74
Diluted-
Diluted (in dollars per share)	$ 0.67	$ 1.02	$ 0.87	$ 0.44	$ 0.20	$ 0.59	$ 0.48	$ 0.20	$ 3.00	$ 1.47	$ 1.72
Increase to provision for income taxes					$ 9,500					$ 9,500

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Subsequent Events (Details) - Subsequent events. - Walker	1 Months Ended
	Feb. 28, 2019 USD ($)
Subsequent Events
Purchase price paid in cash	$ 178,000,000
Promissory note payable	25,000,000
Number of equal installments	2
Installment amount on third and fourth anniversaries	$ 12,500,000