Comfort Systems USA (FIX) 10-K 23 Feb 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Feb. 18, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	1-13011
Entity Registrant Name	Comfort Systems USA, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	76-0526487
Entity Address, Address Line One	675 Bering Drive
Entity Address, Address Line Two	Suite 400
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77057
City Area Code	713
Local Phone Number	830-9600
Title of 12(b) Security	Common Stock, $.01 par value
Trading Symbol	FIX
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float				$ 2,790
Entity Common Stock, Shares Outstanding			35,956,839
Entity Central Index Key	0001035983
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Amendment Flag	false
ICFR Auditor Attestation Flag	true
Auditor Name	Deloitte & Touche LLP	Ernst & Young LLP
Auditor Firm ID	34	42
Auditor Location	Houston, Texas	Houston, Texas

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 58,776	$ 54,896
Billed accounts receivable, less allowance for credit losses of $8,808 and $9,087, respectively	773,716	619,544
Unbilled accounts receivable, less allowance for credit losses of $715 and $784, respectively	61,881	45,596
Other receivables, less allowance for credit losses of $503 and $759, respectively	57,491	44,212
Inventories	21,853	13,472
Prepaid expenses and other	23,704	15,510
Costs and estimated earnings in excess of billings, less allowance for credit losses of $84 and $79, respectively	29,900	18,622
Total current assets	1,027,321	811,852
PROPERTY AND EQUIPMENT, NET	128,554	117,206
LEASE RIGHT-OF-USE ASSET	124,756	94,727
GOODWILL	592,114	464,392
IDENTIFIABLE INTANGIBLE ASSETS, NET	304,781	231,807
DEFERRED TAX ASSETS	22,905	29,401
OTHER NONCURRENT ASSETS	8,683	7,970
Total assets	2,209,114	1,757,355
CURRENT LIABILITIES:
Current maturities of long-term debt	2,788
Accounts payable	254,788	204,145
Accrued compensation and benefits	129,971	121,864
Billings in excess of costs and estimated earnings	307,380	226,237
Accrued self-insurance	22,227	49,166
Other current liabilities	119,400	91,492
Total current liabilities	836,554	692,904
LONG-TERM DEBT, NET	385,242	235,733
LEASE LIABILITIES	107,701	80,576
DEFERRED TAX LIABILITIES	1,745	1,339
OTHER LONG-TERM LIABILITIES	72,206	50,374
Total liabilities	1,403,448	1,060,926
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, 5,032,311 and 4,935,186 shares, respectively	(150,580)	(129,243)
Additional paid-in capital	327,061	322,451
Retained earnings	628,774	502,810
Total stockholders' equity	805,666	696,429
Total liabilities and stockholders' equity	$ 2,209,114	$ 1,757,355

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
CONSOLIDATED BALANCE SHEETS
Billed accounts receivable, allowance for credit losses (in dollars)	$ 8,808	$ 9,087
Unbilled accounts receivable, allowance for credit losses (in dollars)	715	784
Other receivables, allowance for credit losses (in dollars)	503	759
Costs and estimated earnings in excess of billings, allowance for credit losses (in dollars)	$ 84	$ 79
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
Preferred stock, shares outstanding	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	5,032,311	4,935,186

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CONSOLIDATED STATEMENTS OF OPERATIONS
REVENUE	$ 3,073,636	$ 2,856,659	$ 2,615,277
COST OF SERVICES	2,510,429	2,309,676	2,113,334
Gross profit	563,207	546,983	501,943
SELLING, GENERAL AND ADMINISTRATIVE EXPENSES	376,309	357,777	340,005
GAIN ON SALE OF ASSETS	(1,540)	(1,445)	(1,701)
Operating income	188,438	190,651	163,639
OTHER INCOME (EXPENSE):
Interest income	24	103	224
Interest expense	(6,196)	(8,385)	(9,317)
Changes in the fair value of contingent earn-out obligations	7,820	9,119	(2,991)
Other	188	52	187
Other income (expense)	1,836	889	(11,897)
INCOME BEFORE INCOME TAXES	190,274	191,540	151,742
PROVISION FOR INCOME TAXES	46,926	41,401	37,418
NET INCOME	$ 143,348	$ 150,139	$ 114,324
INCOME PER SHARE:
Basic	$ 3.95	$ 4.11	$ 3.10
Diluted	$ 3.93	$ 4.09	$ 3.08
SHARES USED IN COMPUTING INCOME PER SHARE:
Basic	36,285	36,542	36,854
Diluted	36,450	36,738	37,131

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Cumulative Effect, Period of Adoption, Adjustment [Member]Retained Earnings (Deficit)	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings (Deficit)	Total
BALANCE at Dec. 31, 2018			$ 411	$ (87,747)	$ 316,479	$ 268,904	$ 498,047
BALANCE (in shares) at Dec. 31, 2018			41,123,365
BALANCE (in shares) at Dec. 31, 2018				(4,229,653)
Increase (Decrease) in Stockholders' Equity
Net income						114,324	114,324
Issuance of Stock:
Issuance of shares for options exercised				$ 2,532	(182)		2,350
Issuance of shares for options exercised (in shares)				114,125
Issuance of restricted stock & performance stock				$ 2,303	(297)		2,006
Issuance of restricted stock & performance stock (in shares)				107,606
Shares received in lieu of tax withholding payment on vested restricted stock				$ (1,498)			(1,498)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)				28,586
Stock-based compensation					4,168		4,168
Dividends						(14,543)	(14,543)
Share repurchase				$ (19,550)			(19,550)
Share repurchase (in shares)				428,940
BALANCE at Dec. 31, 2019			$ 411	$ (103,960)	320,168	368,685	585,304
BALANCE (in shares) at Dec. 31, 2019			41,123,365
BALANCE (in shares) at Dec. 31, 2019				(4,465,448)
Increase (Decrease) in Stockholders' Equity
Net income						150,139	150,139
Issuance of Stock:
Issuance of shares for options exercised				$ 2,811	(667)		2,144
Issuance of shares for options exercised (in shares)				113,731
Issuance of restricted stock & performance stock				$ 3,102	(1,247)		1,855
Issuance of restricted stock & performance stock (in shares)				128,889
Shares received in lieu of tax withholding payment on vested restricted stock				$ (1,076)			(1,076)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)				27,724
Stock-based compensation					4,197		4,197
Dividends						(15,499)	(15,499)
Share repurchase				$ (30,120)			(30,120)
Share repurchase (in shares)				684,634
BALANCE at Dec. 31, 2020	$ (515)	$ (515)	$ 411	$ (129,243)	322,451	502,810	$ 696,429
BALANCE (in shares) at Dec. 31, 2020			41,123,365				41,123,365
BALANCE (in shares) at Dec. 31, 2020				(4,935,186)			4,935,186
Increase (Decrease) in Stockholders' Equity
Net income						143,348	$ 143,348
Issuance of Stock:
Issuance of shares for options exercised				$ 5,399	235		5,634
Issuance of shares for options exercised (in shares)				195,724
Issuance of restricted stock & performance stock				$ 2,681	(473)		2,208
Issuance of restricted stock & performance stock (in shares)				101,360
Shares received in lieu of tax withholding payment on vested restricted stock				$ (2,363)			(2,363)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)				31,413
Stock-based compensation					4,848		4,848
Dividends						(17,384)	(17,384)
Share repurchase				$ (27,054)			(27,054)
Share repurchase (in shares)				362,796
BALANCE at Dec. 31, 2021			$ 411	$ (150,580)	$ 327,061	$ 628,774	$ 805,666
BALANCE (in shares) at Dec. 31, 2021			41,123,365				41,123,365
BALANCE (in shares) at Dec. 31, 2021				(5,032,311)			5,032,311

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
Dividends (per share)	$ 0.48	$ 0.425	$ 0.395

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 143,348	$ 150,139	$ 114,324
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization of identifiable intangible assets	40,505	32,698	27,082
Depreciation expense	28,439	27,931	24,490
Change in right-of-use assets	17,592	16,692	16,887
Bad debt expense (benefit)	(1,452)	5,253	2,978
Deferred tax provision (benefit)	6,902	(7,953)	(4,251)
Amortization of debt financing costs	538	544	387
Gain on sale of assets	(1,540)	(1,445)	(1,701)
Changes in the fair value of contingent earn-out obligations	(7,820)	(9,119)	2,991
Stock-based compensation	10,593	6,934	5,878
(Increase) decrease in-
Receivables, net	(58,046)	38,486	(49,508)
Inventories	(5,651)	(1,457)	2,366
Prepaid expenses and other current assets	(8,623)	(4,855)	(15,519)
Costs and estimated earnings in excess of billings and unbilled accounts receivable	(17,271)	2,706	(4,312)
Other noncurrent assets	(1,174)	(1,373)	(735)
Increase (decrease) in-
Accounts payable and accrued liabilities	4,004	11,087	31,046
Billings in excess of costs and estimated earnings	44,620	19,434	4,376
Other long-term liabilities	(14,813)	808	(14,751)
Net cash provided by operating activities	180,151	286,510	142,028
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(22,330)	(24,131)	(31,750)
Proceeds from sales of property and equipment	3,101	2,270	2,159
Proceeds from sale of business			1,611
Cash paid for acquisitions, net of cash acquired	(227,493)	(185,941)	(196,470)
Net cash used in investing activities	(246,722)	(207,802)	(224,450)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility	275,000	268,000	356,000
Payments on revolving credit facility	(125,000)	(226,000)	(228,000)
Payments on term loan	(15,000)	(15,000)
Payments on other debt	(15,696)	(46,534)	(3,784)
Payments on finance lease liabilities	(3,805)
Debt financing costs			(1,405)
Payments of dividends to stockholders	(17,384)	(15,499)	(14,543)
Share repurchase	(27,054)	(30,120)	(19,550)
Shares received in lieu of tax withholding	(2,363)	(1,076)	(1,498)
Proceeds from exercise of options	5,634	2,144	2,350
Deferred acquisition payments	(400)	(650)	(637)
Payments for contingent consideration arrangements	(3,481)	(9,865)	(1,343)
Net cash provided by (used in) financing activities	70,451	(74,600)	87,590
NET INCREASE IN CASH AND CASH EQUIVALENTS	3,880	4,108	5,168
CASH AND CASH EQUIVALENTS, beginning of period	54,896	50,788	45,620
CASH AND CASH EQUIVALENTS, end of period	$ 58,776	$ 54,896	$ 50,788

Business and Organization

Business and Organization	12 Months Ended
	Dec. 31, 2021
Business and Organization
Business and Organization	1. Business and Organization Comfort Systems USA, Inc., a Delaware corporation, provides comprehensive mechanical and electrical contracting services, which principally includes heating, ventilation and air conditioning (“HVAC”), plumbing, electrical, piping and controls, as well as off-site construction, monitoring and fire protection. We build, install, maintain, repair and replace mechanical, electrical and plumbing (“MEP”) systems throughout the United States. Approximately 46.3% of our consolidated 2021 revenue is attributable to installation of systems in newly constructed facilities, with the remaining 53.7% 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 Accounti

Summary of Significant Accounting Policies and Estimates	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies and Estimates
Summary of Significant Accounting Policies and Estimates	2. Summary of Significant Accounting Policies and Estimates 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 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, self-insurance accruals, deferred tax assets, 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, ​ 2021 2020 2019 Interest ​ $ 6,052 ​ $ 7,684 ​ $ 8,817 ​ Income taxes, net of refunds ​ $ 52,204 ​ $ 51,286 ​ $ 45,288 ​ Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements ​ In December 2019, the FASB issued ASU No. 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes.” This standard simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in Topic 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The standard also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. ASU No. 2019-12 is effective for fiscal years beginning after December 15, 2020 and interim periods within that year. We adopted ASU No. 2019-12 on January 1, 2021, and the impact was not material to our overall financial statements. ​ Recent Accounting Pronouncements Not Yet Adopted ​ In March 2020, the FASB issued ASU No. 2020-04, “Reference Rate Reform (Topic 848).” The pronouncement provides temporary optional expedients and exceptions to the current guidance on contract modifications and hedge accounting to ease the financial reporting burden related to the expected market transition from the London Interbank Offered Rate (“LIBOR”) and other interbank offered rates to alternative reference rates. The guidance was effective upon issuance and generally can be applied to applicable contract modifications through December 31, 2022. Our current debt facility (as further described in Note 9) includes a Eurodollar Rate Loan Option with an interest rate that is determined based on the one- to six-month LIBOR rates, which will cease to be published on June 30, 2023. We are currently evaluating the impact of the transition from LIBOR to alternative reference rates but do not expect a significant impact to our consolidated financial statements. ​ In October 2021, the FASB issued ASU 2021-08, “Business Combinations (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers.” This standard requires an acquirer to apply Accounting Standards Codification Topic 606 to recognize and measure contract assets and contract liabilities in a business combination. ASU 2021-08 is effective for fiscal years beginning after December 15, 2022 and interim periods within that year. Early adoption is permitted. We are currently evaluating the potential impact of this authoritative guidance on our consolidated financial statements. ​ Revenue Recognition 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, for delivery of 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, 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 construction 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. Our revenue recognition policy is further discussed in Note 3 “Revenue from Contracts with Customers.” ​ Accounts Receivable and Allowance for Credit Losses ​ We are required to estimate and record the expected credit losses over the contractual life of our financial assets measured at amortized cost, including billed and unbilled accounts receivable, other receivables and costs and estimated earnings in excess of billings. Accounts receivable include amounts from work completed in which we have billed or have an unconditional right to bill our customers. Our trade receivables are contractually due in less than a year. ​ We estimate our credit losses using a loss-rate method for each of our identified portfolio segments. Our portfolio segments are construction, service and other. While our construction and service financial assets are often with the same subset of customers and industries, our construction financial assets will generally have a lower loss-rate than service financial assets due to lien rights, which we are more likely to have on construction jobs. These lien rights result in lower credit loss expenses on average compared to receivables that do not have lien rights. Financial assets classified as Other include receivables that are not related to our core revenue producing activities, such as receivables related to our acquisition activity from former owners, our vendor rebate program or receivables for estimated losses in excess of our insurance deductible, which are accrued with a corresponding accrued insurance liability. ​ Loss rates for our portfolios are based on numerous factors, including our history of credit loss expense by portfolio, the financial strength of our customers and counterparties in each portfolio, the aging of our receivables, our expectation of likelihood of payment, macroeconomic trends in the U.S. and the current and forecasted non-residential construction market trends in the U.S. ​ In addition to the loss-rate calculations discussed above, we also record allowance for credit losses for specific receivables that are deemed to have a higher risk profile than the rest of the respective pool of receivables (e.g., when we hold concerns about a specific customer going bankrupt and no longer being able to pay the receivables due to us). ​ Starting in March 2020, we experienced negative impacts to our business due to the disruption caused by Coronavirus Disease 2019 (“COVID-19”). In March 2020, the World Health Organization categorized COVID-19 as a pandemic, and the President of the United States declared the COVID-19 outbreak a national emergency. The Company considered the impact of COVID-19 on the assumptions and estimates used to determine the results reported and asset valuations as of December 31, 2021 and December 31, 2020. ​ In 2020, we increased our loss rates and increased our specific reserves primarily due to the economic disruption caused by COVID-19, which was reflected in our bad debt expense in the prior year. This increase was primarily, but not exclusively, due to concern over collectability of receivables from customers more directly impacted by COVID-19. In 2021, we collected some of these reserve amounts and reduced our assessed risk on collectability as business impacts relating to COVID-19 have stabilized. ​ Activity in our allowance for credit losses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Year Ended December 31, ​ 2021 ​ 2020 ​ Service ​ Construction ​ Other ​ Total ​ Service ​ Construction ​ Other ​ Total Balance at beginning of year $ 4,637 ​ $ 6,028 ​ $ 44 ​ $ 10,709 ​ $ 3,192 ​ $ 3,400 ​ $ 315 ​ $ 6,907 Impact of new accounting standard ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ 310 ​ ​ 331 ​ ​ 54 ​ ​ 695 Bad debt expense (benefit) ​ (970) ​ ​ (496) ​ ​ 14 ​ ​ (1,452) ​ ​ 2,566 ​ ​ 2,697 ​ ​ (10) ​ ​ 5,253 Deductions for uncollectible receivables written off, net of recoveries ​ (742) ​ ​ (244) ​ ​ — ​ ​ (986) ​ ​ (1,431) ​ ​ (735) ​ ​ — ​ ​ (2,166) Credit allowance of acquired receivables on the acquisition date ​ 369 ​ ​ 1,470 ​ ​ — ​ ​ 1,839 ​ ​ — ​ ​ 335 ​ ​ — ​ ​ 335 Reclass to other current liabilities ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ (315) ​ ​ (315) Balance at end of period $ 3,294 ​ $ 6,758 ​ $ 58 ​ $ 10,110 ​ $ 4,637 ​ $ 6,028 ​ $ 44 ​ $ 10,709 ​ 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. 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. We perform a goodwill impairment review for each of our operating units, as we have determined that each of our operating units are 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, or if we elect to perform a quantitative assessment, 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 or their useful lives. Long-Lived Assets Long-lived assets are comprised principally of identifiable intangible assets, property and equipment, lease right-of-use assets 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 undiscounted 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 Contingent Assets and Liabilities 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, such as workers’ compensation, auto liability and general liability, are reviewed by a third-party actuary quarterly. Our self-insurance arrangements are further discussed in Note 13 “Commitments and Contingencies.” Warranty Costs We typically warrant labor for the first year after installation on new MEP systems that we build and install, and we pass through to the customer manufacturers’ warranties on equipment. We generally warrant labor for thirty days after servicing existing MEP 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, uncertain tax positions, and accounting for losses associated with underperforming operations. ​ 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. 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 record unrecognized tax benefits as liabilities when, despite our belief that our tax return positions are supportable, we believe that some portion of our uncertain tax positions may be disallowed. When facts and circumstances change, we adjust these liabilities 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 are accrued and classified as a component in the provision for income taxes in our Consolidated Statements of Operations. 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 related to 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 credit losses. We have a diverse customer base, with our top customer representing 9% of consolidated 2021 revenue. Financial Instruments Our financial instruments consist of cash and cash equivalents, accounts receivable, other receivables, accounts payable, interest rate swaps and life insurance policies, for which we deem the carrying values approximate their fair value due to the short-term nature of these instruments, as well as notes to former owners, a revolving credit facility and a term loan. We believe the carrying value of our debt associated with our senior credit facility approximates its fair value due to the variable rate on such debt. Insurance Recovery We recorded a $4.8 million gain in the fourth quarter of 2019 due to insurance proceeds we received in the fourth quarter. Approximately $1.6 million of the gain was recorded as a reduction in SG&A, and the remainder was recorded as a reduction in Cost of Services expense. These proceeds related to recoverable costs that were primarily incurred prior to the fourth quarter in 2019.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2021
Revenue from Contract with Customers
Revenue from Contracts with Customers	3. Revenue from Contracts with Customers 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 mechanical and electrical contracting services. Our mechanical segment principally includes HVAC, plumbing, piping and controls, as well as off‑ site construction, monitoring and fire protection. Our electrical segment includes installation and servicing of electrical systems. 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, normally installed shortly after receipt and is a value-added element to our work. 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 in our Consolidated 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 obtainment or fulfillment costs in our Consolidated Balance Sheet and have not incurred 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 our Consolidated 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 Consolidated 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 Consolidated Balance Sheet under the caption “Billings in excess of costs and estimated earnings.” Contracts in progress are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 Costs incurred on contracts in progress ​ $ 3,723,715 ​ $ 3,103,580 ​ Estimated earnings, net of losses ​ 589,286 ​ 548,435 ​ Less—Billings to date ​ (4,527,801) ​ (3,813,171) ​ Less—Unbilled accounts receivable ​ ​ (61,881) ​ ​ (45,596) ​ Less—Unbilled accounts receivable credit allowance ​ ​ (715) ​ ​ (784) ​ ​ ​ $ (277,396) ​ $ (207,536) ​ ​ ​ ​ ​ ​ ​ ​ ​ Costs and estimated earnings in excess of billings ​ $ 29,900 ​ $ 18,622 ​ Plus—Costs and estimated earnings in excess of billings credit allowance ​ ​ 84 ​ ​ 79 ​ Billings in excess of costs and estimated earnings ​ (307,380) ​ (226,237) ​ ​ ​ $ (277,396) ​ $ (207,536) ​ ​ 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, 2021 and 2020 were $139.5 million and $124.1 million, respectively, and are included in accounts receivable. Accounts payable at December 31, 2021 and 2020 included $24.0 million and $22.2 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 there is an agreement between the customer and us that the customer pays an additional or reduced 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. The amount of revenue associated with unapproved change orders and claims was immaterial for the year ended December 31, 2021. Variations from estimated project costs could have a significant impact on our operating results, depending on project size, and the recoverability of the variation from change orders collected from customers. 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 30 A performance obligation is a promise in a contract to transfer a distinct good or service to the customer. 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 such cases, 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. In our mechanical segment, 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. ​ We include estimated amounts of variable consideration in the contract price to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Our estimates of variable consideration and determinatio 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 when 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, meaning we recognize 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 in which 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 in our Consolidated Balance Sheet to cover our current estimated outstanding warranty obligations. During the years ended December 31, 2021 and December 31, 2020, net revenue recognized from our performance obligations satisfied in previous periods was not material. ​ Disaggregation of Revenue Our consolidated 2021 revenue was derived from contracts to provide service activities in the mechanical and electrical services segments we serve. Refer to Note 16 “Segment Information” for additional information on our reportable segments. We disaggregate our revenue from contracts with customers by activity, customer type and service provided, as we believe it best depicts how the nature, amount, timing and uncertainty of our revenue and cash flows are affected by economic factors. See details in the following tables (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Revenue by Service Provided 2021 ​ 2020 ​ ​ 2019 ​ Mechanical Services ​ ​ $ 2,542,623 82.7 % ​ $ 2,430,632 85.1 % ​ $ 2,272,031 ​ 86.9 % Electrical Services ​ ​ ​ 531,013 ​ 17.3 % ​ ​ 426,027 ​ 14.9 % ​ ​ 343,246 ​ 13.1 % Total ​ ​ $ 3,073,636 ​ 100.0 % ​ $ 2,856,659 ​ 100.0 % ​ $ 2,615,277 ​ 100.0 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Revenue by Type of Customer ​ ​ 2021 ​ ​ 2020 ​ 2019 Industrial ​ ​ $ 1,356,688 ​ 44.1 % ​ $ 1,112,075 ​ 38.9 % ​ $ 886,668 ​ 33.9 % Education ​ ​ ​ 390,251 ​ 12.7 % ​ ​ 487,922 ​ 17.1 % ​ ​ 412,318 ​ 15.8 % Office Buildings ​ ​ ​ 308,799 ​ 10.1 % ​ ​ 319,426 ​ 11.2 % ​ ​ 348,640 ​ 13.3 % Healthcare ​ ​ ​ 417,901 ​ 13.6 % ​ ​ 371,105 ​ 13.0 % ​ ​ 358,155 ​ 13.7 % Government ​ ​ ​ 174,813 ​ 5.7 % ​ ​ 163,717 ​ 5.7 % ​ ​ 162,507 ​ 6.2 % Retail, Restaurants and Entertainment ​ ​ ​ 213,386 ​ 6.9 % ​ ​ 239,541 ​ 8.4 % ​ ​ 248,083 ​ 9.5 % Multi-Family and Residential ​ ​ ​ 112,779 ​ 3.7 % ​ ​ 86,799 ​ 3.0 % ​ ​ 104,693 ​ 4.0 % Other ​ ​ ​ 99,019 ​ 3.2 % ​ ​ 76,074 ​ 2.7 % ​ ​ 94,213 ​ 3.6 % Total ​ ​ $ 3,073,636 ​ 100.0 % ​ $ 2,856,659 ​ 100.0 % ​ $ 2,615,277 ​ 100.0 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Revenue by Activity Type ​ ​ 2021 ​ ​ 2020 ​ 2019 ​ New Construction ​ ​ $ 1,421,784 ​ 46.3 % ​ $ 1,333,739 ​ 46.7 % ​ $ 1,201,122 ​ 45.9 % Existing Building Construction ​ ​ ​ 963,461 ​ 31.3 % ​ ​ 910,807 ​ 31.9 % ​ ​ 793,159 ​ 30.3 % Service Projects ​ ​ ​ 278,582 ​ 9.1 % ​ ​ 241,402 ​ 8.4 % ​ ​ 231,228 ​ 8.9 % Service Calls, Maintenance and Monitoring ​ ​ ​ 409,809 ​ 13.3 % ​ ​ 370,711 ​ 13.0 % ​ ​ 389,768 ​ 14.9 % Total ​ ​ $ 3,073,636 ​ 100.0 % ​ $ 2,856,659 ​ 100.0 % ​ $ 2,615,277 ​ 100.0 % ​ 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, revenue recognized exceeds the amount billed to the customer and right to payment is conditional or 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 and liabilities 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. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ Year Ended December 31, ​ 2021 ​ 2020 ​ Contract Contract ​ Contract Contract ​ Assets ​ Liabilities ​ Assets ​ Liabilities Balance at beginning of period $ 18,622 ​ $ 226,237 ​ $ 2,736 ​ $ 166,918 Change due to acquisitions / disposals ​ 10,356 ​ ​ 36,523 ​ ​ 9,509 ​ ​ 39,885 Change related to credit allowance ​ (5) ​ ​ — ​ ​ (79) ​ ​ — Other changes in the period ​ 927 ​ ​ 44,620 ​ ​ 6,456 ​ ​ 19,434 Balance at end of period $ 29,900 ​ $ 307,380 ​ $ 18,622 $ 226,237 ​ During the years ended December 31, 2021 and 2020, we recognized revenue of $207.6 million and $165.8 million related to our contract liabilities at January 1, 2021 and January 1, 2020, respectively. ​ We did not have any impairment losses recognized on our receivables or contract assets in 2021 and 2020. ​ Remaining Performance Obligations ​ Remaining construction performance obligations represent the remaining transaction price of firm orders for which work has not been performed and exclude unexercised contract options. As of December 31, 2021, the aggregate amount of the transaction price allocated to remaining performance obligations was $2.31 billion. The Company expects to recognize revenue on approximately 80-85% 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 with a total term of one year or less; therefore, we do not report unfulfilled performance obligations for service maintenance agreements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
Fair Value Measurements
Fair Value Measurements	4. Fair Value Measurements Interest Rate Risk Management and Derivative Instruments ​ In April 2020, we entered into interest rate swap agreements to reduce our exposure to variable interest rates on our term loan and revolving credit facility. The notional amount covered by these interest rate swaps was $80.0 million as of December 31, 2021, and the termination date is September 30, 2022. ​ We use derivative instruments to manage exposure to market risk, including interest rate risk. Unsettled amounts under our interest rate swaps are recorded in the Consolidated Balance Sheet at fair value in “Other Receivables” or “Other Current Liabilities.” Gains and losses on our interest rate swaps are recorded in the Consolidated Income Statement in “Interest Expense.” For the years ended December 31, 2021 and December 31, 2020, we recognized a net loss of $0.5 million and $0.3 million, respectively, related to our interest rate swaps. We currently do not have any derivatives that are accounted for as hedges under ASC 815. ​ Fair Value Measurement ​ 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 are included, for assets and liabilities measured on a recurring basis as of December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2021 ​ Level 1 Level 2 Level 3 Total Cash and cash equivalents ​ $ 58,776 ​ $ — ​ $ — ​ $ 58,776 Life insurance—cash surrender value ​ $ — ​ $ 6,643 ​ $ — ​ $ 6,643 Contingent earn-out obligations ​ $ — ​ $ — ​ $ 34,114 ​ $ 34,114 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2020 ​ Level 1 Level 2 Level 3 Total Cash and cash equivalents ​ $ 54,896 ​ $ — ​ $ — ​ $ 54,896 Life insurance—cash surrender value ​ $ — ​ $ 5,420 ​ $ — ​ $ 5,420 Contingent earn-out obligations ​ $ — ​ $ — ​ $ 25,979 ​ $ 25,979 Interest rate swap liability ​ $ — ​ $ 42 ​ $ — ​ $ 42 ​ 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 fair value for our interest rate swaps is based upon inputs corroborated by observable market data with similar tenors, which are considered Level 2 inputs. The Company’s outstanding term loan held by third-party financial institutions is carried at cost, adjusted for debt issuance costs. The Company’s term loan is not publicly traded and the carrying amount approximates fair value as the loan accrues interest at a variable rate. 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 85 employees with a combined face value of $62.3 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 was $6.6 million as of December 31, 2021 and $5.4 million as of December 31, 2020. 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 and operating income, probabilities of achieving such future cash flows and operating income and a weighted average cost of capital. Significant changes in any of these assumptions could result in a significantly higher or lower potential liability. The contingent earn-out obligations are measured at fair value each reporting period, and changes in estimates of fair value are recognized in earnings. As of December 31, 2021, cash flows were discounted using a weighted average cost of capital ranging from 10.0% - 16.5%. 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, ​ ​ 2021 2020 Balance at beginning of year $ 25,979 $ 28,497 Issuances ​ 19,949 ​ 16,715 ​ Settlements ​ ​ (3,994) ​ ​ (10,114) ​ Adjustments to fair value ​ (7,820) ​ (9,119) ​ Balance at end of year ​ $ 34,114 ​ $ 25,979 ​ ​ We measure certain assets at fair value on a nonrecurring basis. These assets are recognized at fair value when they are concluded to be other-than-temporarily impaired. No goodwill or other intangible asset impairments were recorded during the years ended December 31, 2021, 2020 and 2019. We did not recognize any other impairments on those assets required to be measured at fair value on a nonrecurring basis. See Note 6 “Goodwill and Identifiable Intangible Assets, Net” for further discussion.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2021
Acquisitions
Acquisitions	5. Acquisitions Amteck Holdco LLC Acquisition ​ On August 1, 2021, we acquired all of the issued and outstanding equity interests of Amteck Holdco LLC and each of its wholly owned subsidiaries (collectively “Amteck”). Amteck provides electrical contracting solutions and services, including design and build, pre-fabrication and installation for core electric and low-voltage systems, as well as services for planned maintenance, retrofit and emergency work. Amteck is headquartered in Kentucky and primarily serves the greater Southeastern United States, including Kentucky, Tennessee and the Carolinas. As a result of the acquisition, Amteck is a wholly owned subsidiary of the Company reported in our electrical services segment. Revenue attributable to Amteck was $83.5 million for the five months from the acquisition date. ​ The following summarizes the acquisition date fair value of consideration transferred and the acquisition date fair value of the identifiable assets acquired and liabilities assumed, including an amount for goodwill (in thousands): ​ ​ ​ ​ Consideration transferred: ​ ​ Cash paid at closing $ 107,355 Working capital adjustment ​ 7,409 Notes issued to former owners ​ 10,000 Estimated fair value of contingent earn-out payments ​ 12,900 ​ $ 137,664 Recognized amounts of identifiable assets acquired and liabilities assumed: ​ ​ Cash and cash equivalents $ 13,554 Billed and unbilled accounts receivable ​ 43,248 Other current assets ​ 3,422 Property and equipment ​ 3,886 Goodwill ​ 55,076 Identifiable intangible assets ​ 57,700 Operating lease right-of-use asset ​ 8,997 Accounts payable ​ (14,489) Billings in excess of costs and estimated earnings ​ (15,199) Current maturities of long-term debt ​ (1,860) Current operating lease liabilities ​ (1,115) Accrued expenses and other current liabilities ​ (6,889) Long-term debt ​ (785) Long-term operating lease liabilities ​ (7,882) ​ $ 137,664 ​ The allocation of the purchase price to the assets acquired and liabilities assumed is preliminary and, therefore, subject to change pending the completion of the final valuation of intangible assets and accrued liabilities. Goodwill represents the future economic benefits arising from other assets acquired that could not be individually identified and separately recognized. All of the goodwill recognized as a result of the Amteck acquisition is tax deductible. ​ In estimating the fair value of the acquired intangible assets, we utilized the valuation methodology determined to be the most appropriate for the individual intangible asset. In order to estimate the fair value of the backlog and customer relationships, we utilized an excess earnings methodology, which consisted of the projected cash flows attributable to these assets discounted to present value using a risk-adjusted discount rate that represented the required rate of return. The trade name value was determined based on the relief-from-royalty method, which applies a royalty rate to the revenue stream attributable to this asset, and the resulting royalty payment is tax effected and discounted to present value. Some of the more significant estimates and assumptions inherent in determining the fair value of the identifiable intangible assets are associated with forecasting cash flows and profitability, which represent Level 3 inputs. The primary assumptions used were generally based upon the present value of anticipated cash flows discounted at rates ranging from 14.0% - 18.5 %. Estimated years of projected earnings generally follow the range of estimated remaining useful lives for each intangible asset class. ​ The acquired intangible assets include the following (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Valuation Method ​ Estimated Useful Life ​ ​ Estimated Fair Value Backlog ​ Excess earnings ​ 1.5 years ​ $ 7,800 Trade Name ​ Relief-from-royalty ​ 23 years ​ ​ 12,600 Customer Relationships ​ Excess earnings ​ 9 years ​ ​ 37,300 Total ​ ​ ​ ​ ​ $ 57,700 ​ The contingent earn-out obligation is associated with the achievement of four earnings milestones over a 53-month period, and the range of each average present value estimated milestone payment is $0.1 million to $11.4 million. We determined the initial fair value of the contingent earn-out obligation based on the Monte Carlo Simulation method, which represents a Level 3 measurement. Cash flows were discounted using discount rates ranging from 14.8% - 15.2%, which we believe is appropriate and representative of a market participant assumption. Subsequent to the acquisition date, the contingent earn-out obligation is remeasured at fair value each reporting period. Changes in the estimated fair value of the contingent payments subsequent to the acquisition date are recognized in earnings. ​ Other Acquisitions ​ On December 31, 2021, we acquired MEP Holding Co., Inc., and its related subsidiaries (collectively, “MEP Holdings”) for a total preliminary purchase price of $57.3 million, which included $45.2 million funded on the closing date, $7.6 million in notes payable to former owners, an earn-out that will be paid if certain financial targets are met after the acquisition date and a working capital adjustment. As a result of the acquisition, MEP Holdings is a wholly owned subsidiary of the Company and reports as a separate operating location in our electrical services segment. Additionally, on December 31, 2021, we completed an acquisition of a service and controls business in Kentucky with a total preliminary purchase price of $21.1 million and a temporary staffing company based in Indiana with a total preliminary purchase price of $4.6 million, which are both reported in our mechanical services segment. ​ On December 1, 2021, we acquired Ivey Mechanical Company, LLC (“Ivey”) headquartered in Kosciusko, Mississippi for a total preliminary purchase price of $78.8 million, which included $64.1 million of cash paid on the closing date, $8.0 million in notes payable to former owners, a $0.4 million short term payable plus an earn-out that will be paid if certain financial targets are met after the acquisition date and a working capital adjustment. As a result of the acquisition, Ivey is a wholly owned subsidiary of the Company and reports as a separate operating location in our mechanical services segment. ​ In the first quarter of 2021, we completed an acquisition of a mechanical contractor in Utah with a total purchase price of $18.1 million, which is reported in our mechanical services segment. ​ In the fourth quarter of 2020, we acquired all outstanding equity interests of Tennessee Electric Company, Inc. dba TEC Industrial Maintenance and Construction (“TEC”) for a total purchase price of $88.9 million, which included $73.0 million in cash, $7.0 million in notes payable to former owners, a $7.6 million contingent earn-out obligation and a $1.3 million working capital adjustment. As a result of the acquisition, TEC is a wholly owned subsidiary of the Company and reports as a separate operating location in our electrical services segment. ​ On April 1, 2020, we consummated a merger through which TAS Energy Inc. (“TAS”) became a wholly owned subsidiary of the Company. The total purchase price was $169.5 million, of which $126.2 million was allocated to goodwill and identifiable intangible assets. The total purchase price included $105.9 million in cash, $40.5 million in working capital adjustment, $14.0 million in notes payable to former owners and a $9.1 million contingent earn-out obligation. TAS is headquartered in Houston, Texas, and is a leading engineering, design and construction provider of modular construction systems serving the technology, power and industrial sectors, and reports as a separate operating location in our mechanical services segment. ​ We completed the acquisition of an electrical contractor in North Carolina in the first quarter of 2020 with a total purchase price of $41.6 million. This acquisition is reported in our electrical services segment. ​ The results of operations of acquisitions are included in our consolidated financial statements from their respective acquisition dates. Our Consolidated Balance Sheet includes preliminary allocations of the purchase price to the assets acquired and liabilities assumed for the applicable acquisitions pending the completion of the final valuation of intangible assets and accrued liabilities. 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 under which continued employment is a condition to receipt of payment, then the earn-out is recorded as compensation expense over the period earned.

Goodwill and Identifiable Intan

Goodwill and Identifiable Intangible Assets, Net	12 Months Ended
	Dec. 31, 2021
Goodwill and Identifiable Intangible Assets, Net
Goodwill and Identifiable Intangible Assets, Net	6. Goodwill and Identifiable Intangible Assets, Net Goodwill The changes in the carrying amount of goodwill are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mechanical Services ​ Electrical Services ​ ​ ​ Segment Segment ​ Total Balance at December 31, 2019 ​ $ 234,660 ​ $ 97,787 ​ $ 332,447 Acquisitions and purchase price adjustments (See Note 5) ​ 72,788 ​ ​ 59,157 ​ ​ 131,945 Balance at December 31, 2020 ​ ​ 307,448 ​ ​ 156,944 ​ ​ 464,392 Acquisitions and purchase price adjustments (See Note 5) ​ ​ 52,771 ​ ​ 74,951 ​ ​ 127,722 Impact of segment reorganization ​ ​ 1,101 ​ ​ (1,101) ​ ​ — Balance at December 31, 2021 ​ $ 361,320 ​ $ 230,794 ​ $ 592,114 ​ The aggregate goodwill balance as of December 31, 2021 and 2020 includes $116.6 million of accumulated impairment charges, all of which relate to the mechanical services segment. 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 and Estimates,” 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, 2021, we performed a qualitative assessment for all of our reporting units except one for which we performed a quantitative assessment, 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 substantially greater than its carrying value. Accordingly, no further testing was required. For our Texas electrical operation, we performed a step 1 quantitative assessment, and the calculated fair value exceeded the carrying value by 32%. As a result of the reporting unit’s smaller excess of fair value percentage, this reporting unit is more susceptible to impairment risk from additional adverse changes in its operating environment, including micro- and macroeconomic environment conditions that could negatively impact them. Such adverse changes could include worsening economic conditions in the locations or markets they primarily serve, whether due to COVID-19 or other events and conditions. As of December 31, 2021, the Texas electrical operation had a goodwill balance of $96.8 million. For the years ended December 31, 2021, 2020 and 2019, no impairment of our goodwill was recorded. 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): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ December 31, 2021 ​ December 31, 2020 ​ Remaining Useful Lives Gross Book Accumulated Gross Book Accumulated ​ in Years Value Amortization Value Amortization Customer Relationships 7.6 ​ $ 330,572 ​ $ (130,098) ​ $ 255,692 ​ $ (103,919) Backlog 1.1 ​ 32,300 ​ (20,091) ​ 19,800 ​ (12,600) Trade Names 19.6 ​ 114,795 ​ (22,697) ​ 91,495 ​ (18,661) Total ​ ​ ​ $ 477,667 ​ $ (172,886) ​ $ 366,987 ​ $ (135,180) ​ The amounts attributable to customer relationships and tradenames are amortized to “Selling, General and Administrative Expenses” based upon the estimated consumption of their economic benefits, or a straight-line method over periods from one As of December 31, 2021, future amortization expense of identifiable intangible assets was as follows (in thousands): ​ ​ ​ ​ ​ Year ending December 31— ​ ​ 2022 ​ $ 46,505 ​ 2023 ​ 34,532 ​ 2024 ​ 32,343 ​ 2025 ​ 30,156 ​ 2026 ​ ​ 29,312 ​ Thereafter ​ 131,933 ​ Total ​ $ 304,781 ​ ​

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2021
Property and Equipment
Property and Equipment	7. Property and Equipment Property and equipment consist of the following (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Estimated ​ ​ ​ ​ ​ ​ ​ Useful Lives December 31, ​ in Years 2021 2020 Land — ​ $ 6,792 ​ $ 7,167 ​ Transportation equipment 1 - 7 ​ 132,792 ​ 113,802 ​ Machinery and equipment 1 - 20 ​ 48,000 ​ 43,386 ​ Computer and telephone equipment 1 - 10 ​ 23,065 ​ 23,215 ​ Buildings and leasehold improvements 1 - 40 ​ 74,981 ​ 69,683 ​ Furniture and fixtures 1 - 17 ​ ​ 6,081 ​ ​ 5,861 ​ Construction in progress — ​ 1,668 ​ 1,294 ​ ​ ​ ​ ​ 293,379 ​ 264,408 ​ Less—Accumulated depreciation ​ ​ ​ (164,825) ​ (147,202) ​ Property and equipment, net ​ ​ ​ $ 128,554 ​ $ 117,206 ​ ​ Depreciation expense for the years ended December 31, 2021, 2020 and 2019 was $28.4 million, $27.9 million and $24.5 million, respectively.

Detail of Other Current Liabili

Detail of Other Current Liabilities	12 Months Ended
	Dec. 31, 2021
Detail of Other Current Liabilities
Detail of Other Current Liabilities	8. Detail of Other Current Liabilities Other current liabilities consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 Accrued warranty costs ​ $ 8,969 ​ $ 8,914 ​ Current lease liability ​ ​ 19,050 ​ ​ 16,586 ​ Accrued job losses ​ 8,962 ​ 2,151 ​ Accrued sales and use tax ​ 3,861 ​ 3,731 ​ Deferred revenue ​ 13,734 ​ 4,559 ​ Liabilities due to former owners ​ 27,613 ​ 10,280 ​ Other current liabilities ​ 37,211 ​ 45,271 ​ ​ ​ $ 119,400 ​ $ 91,492 ​ ​

Debt Obligations

Debt Obligations	12 Months Ended
	Dec. 31, 2021
Debt Obligations
Debt Obligations	9. Debt Obligations Debt obligations consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2021 2020 Revolving credit facility ​ $ 220,000 ​ $ 70,000 ​ Term loan ​ ​ 120,000 ​ ​ 135,000 ​ Notes to former owners ​ ​ 47,954 ​ 31,000 ​ Finance lease liabilities (See Note 10) ​ ​ 266 ​ ​ — ​ Total principal amount ​ ​ 388,220 ​ 236,000 ​ Less—unamortized debt issuance costs ​ ​ (190) ​ ​ (267) ​ Total debt, net of unamortized debt issuance costs ​ ​ 388,030 ​ ​ 235,733 ​ Less—current portion ​ ​ (2,788) ​ — ​ Total long-term portion of debt, net ​ $ 385,242 ​ $ 235,733 ​ ​ At December 31, 2021, future principal payments of debt are as follows (in thousands): ​ ​ ​ ​ ​ Year ending December 31— ​ ​ 2022 $ 2,788 2023 ​ 27,981 ​ 2024 ​ 35,352 ​ 2025 ​ 322,099 ​ ​ ​ $ 388,220 ​ ​ Interest expense included the following primary elements (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 2019 Interest expense on notes to former owners ​ $ 1,052 ​ $ 1,354 ​ $ 1,531 ​ Interest expense on borrowings and unused commitment fees ​ 3,371 ​ 5,319 ​ 6,887 ​ Interest expense on interest rate swaps ​ ​ 499 ​ ​ 338 ​ ​ — ​ Interest expense on finance leases ​ ​ 57 ​ ​ — ​ ​ — ​ Letter of credit fees ​ 679 ​ 830 ​ 512 ​ Amortization of debt financing costs ​ 538 ​ 544 ​ 387 ​ Total ​ $ 6,196 ​ $ 8,385 ​ $ 9,317 ​ ​ Revolving Credit Facility and Term Loan We have a $600.0 million senior credit facility (the “Facility”) provided by a syndicate of banks. The Facility is composed of a revolving credit line in the amount of $450.0 million and a $150.0 million term loan, and the Facility provides for a $150.0 million accordion or increase option for the revolving portion of the Facility. As of December 31, 2021, the Facility capacity was $570.0 million, as the term loan was paid down by $30.0 million since the inception of the Facility. The amended Facility also includes a sublimit of up to $160.0 million issuable in the form of letters of credit. The Facility expires in January 2025 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 our wholly owned captive insurance company, and a second lien on our assets related to projects subject to surety bonds. In 2019, we incurred approximately $1.4 million in financing and professional costs in connection with an amendment to the Facility, which are being amortized over the remaining term of the Facility. Of this amount, $0.4 million is attributable to the term loan and is being amortized using the effective interest method. For the term loan, we are required to make quarterly payments increasing over time from 1.25% to 3.75% of the original aggregate principal amount of the term loan, with the balance due in January 2025. As of December 31, 2021, we had $120.0 million principal outstanding on the term loan, $220.0 million of outstanding borrowings on the revolving credit facility, $53.5 million in letters of credit outstanding and $176.5 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, 2021, the book value of these assets was approximately $98.9 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 Facility’s principal financial covenants include: Total Leverage Ratio— Fixed Charge Coverage Ratio— Other Restrictions— 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, 2021. 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,” which shall mean Consolidated EBITDA as such term is defined in the credit agreement, for the twelve months ending as of that quarter end. 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, 2021 relating to interest options under the Facility: ​ ​ ​ ​ Base Rate Loan Option: Federal Funds Rate plus 0.50% 0.57% ​ Wells Fargo Bank, N.A. Prime Rate ​ 3.25% ​ One-month LIBOR plus 1.00% ​ 1.10% ​ Eurodollar Rate Loan Option: ​ ​ ​ One-month LIBOR ​ 0.10% ​ Six-month LIBOR ​ 0.34% ​ ​ 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 a 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. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 revolving credit facility was approximately 1.4% as of December 31, 2021. The weighted average interest rate applicable to the term loan was approximately 1.4% as of December 31, 2021. Notes to Former Owners As part of the consideration used to acquire ten companies, we have outstanding notes to the former owners. Together, these notes had an outstanding balance of $48.0 million as of December 31, 2021. In conjunction with the acquisition of MEP Holdings in the fourth quarter of 2021, we issued a promissory note to former owners with an outstanding balance of $7.6 million as of December 31, 2021 that bears interest, payable quarterly, at a stated interest rate of 2.5%. The principal is due in equal installments in April 2024 and April 2025. In conjunction with the acquisition of Ivey in the fourth quarter of 2021, we issued a promissory note to former owners with an outstanding balance of $8.0 million as of December 31, 2021 that bears interest, payable quarterly, at a stated interest rate of 2.5%. The principal is due in January 2025. In conjunction with the acquisition of Amteck in the third quarter of 2021, we issued a promissory note to former owners with an outstanding balance of $10.0 million as of December 31, 2021 that bears interest, payable quarterly, at a stated interest rate of 2.5%. The principal is due in equal installments in October 2024 and October 2025. In conjunction with the acquisition of a Texas electrical contractor in the second quarter of 2019, we issued a promissory note to former owners with an outstanding balance of $2.0 million as of December 31, 2021 that bears interest, payable quarterly, at a stated interest rate of 4.0%. The remaining principal is due in April 2023. In conjunction with the six remaining acquisitions, we issued notes to former owners with an outstanding balance of $20.4 million as of December 31, 2021 that bear interest, payable quarterly, at stated interest rates ranging from 2.3% - 3.5%. The principal amounts are due between April 2022 and April 2025.

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases
Leases	10. Leases We lease certain facilities, vehicles and equipment primarily under noncancelable operating leases. The most significant portion of these noncancelable operating leases are for the facilities occupied by our corporate office and our operating locations. We have finance leases on vehicles that are not material to our consolidated financial position. As of December 31, 2021, the lease liabilities associated with these finance leases ​ The lease terms generally range from three ​ A majority of the Company’s real property leases are with individuals or entities with whom we have no other business relationship. However, in certain instances the Company enters into real property leases with current or former employees. Rent paid to related parties for the years ended December 31, 2021, 2020 and 2019 was approximately $4.9 million, $4.2 million and $3.7 million, respectively. ​ If we decide to cancel or terminate a lease before the end of its term, we would typically owe the lessor the remaining lease payments under the term of the lease. Our lease agreements do not contain any material residual value guarantees or material restrictive covenants. On rare occasions, we rent or sublease certain real estate assets that we no longer use to third parties. ​ Finance lease right-of-use assets are included in “Property and equipment, net,” and current and long-term finance lease liabilities are included within “Current maturities of long-term debt” and “Long-term debt, net,” respectively, in the Consolidated Balance Sheet. The following table summarizes the operating lease assets and liabilities included in the Consolidated Balance Sheet as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 ​ December 31, 2020 Operating lease right-of-use assets $ 124,756 ​ $ 94,727 Operating lease liabilities: ​ ​ ​ ​ ​ Other current liabilities $ 19,050 ​ $ 16,586 Long-term operating lease liabilities ​ 107,701 ​ ​ 80,576 Total operating lease liabilities $ 126,751 ​ $ 97,162 ​ The maturities of operating lease liabilities as of December 31, 2021 are as follows (in thousands): ​ ​ ​ ​ ​ Year ending December 31— ​ ​ ​ 2022 ​ $ 23,729 2023 ​ ​ 21,142 2024 ​ ​ 18,738 2025 ​ ​ 17,642 2026 ​ ​ 14,631 Thereafter ​ ​ 55,161 Total Lease Payments ​ ​ 151,043 Less—Present Value Discount ​ ​ (24,292) Present Value of Operating Lease Liabilities ​ $ 126,751 ​ Supplemental information related to operating leases was as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 ​ 2020 Cash paid for amounts included in the measurement of operating lease liabilities $ 22,232 ​ $ 20,443 Operating lease right-of-use assets obtained in exchange for lease liabilities $ 47,621 ​ $ 27,346 ​

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Taxes
Income Taxes	​ 11. Income Taxes Provision for Income Taxes Our provision for income taxes relating to continuing operations consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 2019 Current tax provision— ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ $ 31,283 ​ $ 36,556 ​ $ 33,281 ​ State ​ 8,741 ​ 12,798 ​ 8,388 ​ Total current ​ 40,024 ​ 49,354 ​ 41,669 ​ Deferred tax provision (benefit)— ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ 6,197 ​ (5,483) ​ (3,750) ​ State ​ 705 ​ (2,470) ​ (501) ​ Total deferred ​ 6,902 ​ (7,953) ​ (4,251) ​ Provision for income taxes ​ $ 46,926 ​ $ 41,401 ​ $ 37,418 ​ ​ The provision for income taxes for the years ended December 31, 2021, 2020 and 2019 resulted in effective tax rates on continuing operations of 24.7%, 21.6% and 24.7%, respectively. The reasons for the differences between these effective tax rates and the federal statutory rates are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 2019 Federal statutory rate of— ​ ​ 21 % ​ 21 % ​ 21 % Income taxes at the federal statutory rate ​ $ 39,958 ​ $ 40,223 ​ $ 31,866 ​ Increases (decreases) resulting from— ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net state income taxes ​ 7,340 ​ 8,406 ​ 6,644 ​ Valuation allowances ​ (39) ​ (254) ​ (279) ​ Net unrecognized tax benefits ​ 640 ​ 18,557 ​ 7,338 ​ Nondeductible expenses ​ 2,381 ​ 2,470 ​ 2,180 ​ R&D tax credit ​ — ​ (26,133) ​ (4,569) ​ 179D deduction ​ ​ (1,207) ​ ​ (1,062) ​ ​ (5,126) ​ Stock-based compensation deductions ​ ​ (2,210) ​ ​ (426) ​ ​ (714) ​ Other ​ 63 ​ (380) ​ 78 ​ Provision for income taxes ​ $ 46,926 ​ $ 41,401 ​ $ 37,418 ​ ​ In the third quarter of 2019, we filed an amended federal return for 2015 to claim the credit for increasing research activities (the “R&D tax credit”) and recorded a $4.6 million tax benefit that was fully offset by an addition to unrecognized tax benefits. We previously filed an amended federal return for 2014 to claim the R&D tax credit during 2018 and recorded a $2.7 million tax benefit that was also fully offset by an addition to unrecognized tax benefits. These $7.3 million of tax benefits were fully offset by additions to unrecognized tax benefits due to the uncertainty of the outcome from examinations opened by the Internal Revenue Service (the “IRS”). As a result, the R&D tax credit claimed had no impact on our effective tax rates. For the year ended December 31, 2019, our provision for income taxes was decreased by $2.2 million due to benefits from the filing, and expected filing, of amended returns to claim the energy efficient commercial buildings deduction (the “179D deduction”) allocated to us. ​ ​ ​ 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, ​ 2021 2020 Deferred tax assets— ​ ​ ​ ​ ​ ​ ​ Accounts receivable and allowance for credit losses ​ $ 1,878 ​ $ 2,186 ​ Stock-based compensation ​ 3,392 ​ 2,791 ​ Accrued liabilities and expenses ​ 36,255 ​ 39,761 ​ Lease liabilities ​ ​ 27,944 ​ ​ 22,768 ​ Net operating loss carryforwards ​ 10,379 ​ 12,127 ​ Intangible assets ​ ​ 3,851 ​ ​ — ​ Other ​ 758 ​ 627 ​ Subtotal ​ 84,457 ​ 80,260 ​ Valuation allowances ​ (475) ​ (514) ​ Total deferred tax assets ​ ​ 83,982 ​ ​ 79,746 ​ Deferred tax liabilities— ​ ​ ​ ​ ​ ​ ​ Property and equipment ​ (15,534) ​ (13,877) ​ Lease right-of-use asset ​ ​ (27,905) ​ ​ (22,715) ​ Long-term contracts ​ (964) ​ (609) ​ Intangible assets ​ ​ — ​ ​ (242) ​ Goodwill ​ (17,321) ​ (11,615) ​ Other ​ (1,098) ​ (2,626) ​ Total deferred tax liabilities ​ (62,822) ​ (51,684) ​ Net deferred tax assets ​ $ 21,160 ​ $ 28,062 ​ ​ The deferred tax assets and liabilities reflected above are included in the Consolidated Balance Sheets as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 Deferred tax assets ​ $ 22,905 ​ $ 29,401 ​ Deferred tax liabilities ​ $ 1,745 ​ $ 1,339 ​ ​ As of December 31, 2021, we had $7.2 million of deferred tax assets related to $34.2 million of federal net operating loss (“NOL”) carryforwards as a result of the TAS acquisition. If not used, such carryforwards will begin to expire in 2031. We also had $3.2 million of deferred tax assets related to $61.7 million of state NOL carryforwards, including carryforwards acquired from TAS. The state NOL carryforwards will expire in varying amounts between the years 2022 and 2041. Pursuant to Section 382 of the Code, utilization of our federal NOL carryforwards is subject to annual limitations due to the ownership change in TAS. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50 percentage points over a three-year period. While we expect to fully utilize the federal NOL carryforwards acquired from TAS before they begin to expire in 2031, valuation allowances were recorded against certain of its state NOL carryforwards. We do not believe it is more-likely-than-not that TAS will have sufficient revenue-generating operations in those states in the future. ​ Valuation allowances of $0.4 million have been recorded against certain of the state NOL carryforwards. The $2.8 million of deferred tax assets 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 of our subsidiaries. We regularly update our assessment of the realizability of our deferred tax assets, in particular, those related to state NOL carryforwards. A return to profitability in our subsidiaries with valuation allowances would result in a release of a portion of the valuation allowances 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, ​ 2021 2020 2019 Balance at beginning of year ​ $ 28,756 ​ $ 10,199 ​ $ 2,966 ​ Additions based on tax positions related to current year ​ 207 ​ — ​ — ​ Additions based on tax positions related to prior years ​ 489 ​ 26,858 ​ 7,473 ​ Reductions for tax positions related to prior years ​ — ​ — ​ (240) ​ Reductions for settlements with tax authorities ​ — ​ (8,301) ​ — ​ Balance at end of year ​ $ 29,452 ​ $ 28,756 ​ $ 10,199 ​ ​ We are subject to taxation in the United States and various state jurisdictions. For the year ended December 31, 2020, our unrecognized tax benefits were reduced by $8.3 million due to a favorable settlement with the IRS for the 2014 and 2015 tax years. As of December 31, 2021, we remain open to IRS examination for the 2017 tax year forward. State income tax returns are generally subject to examination for a period of three to four years after filing the returns. However, the state impact of any federal audit adjustments and/or amendments remains subject to examination by various states for up to one year after formal notification to the states. As of December 31, 2021, we generally remain open to examination by various state tax authorities for the 2017 tax year forward. We will have a reduction of $28.8 million in unrecognized tax benefits in the first quarter of 2022 due to a favorable settlement with the IRS for the 2016, 2017 and 2018 tax years. Any further reductions in our unrecognized tax benefits, due to the future recognition of those tax benefits, would affect our effective tax rates.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2021
Employee Benefit Plans
Employee Benefit Plans	12. 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 $16.1 million in 2021, $16.3 million in 2020 and $14.2 million in 2019. Of these amounts, approximately $0.6 million and $0.5 million were payable to the plans at December 31, 2021 and 2020, 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, 2021 and 2020, we had 5 and 6, respectively, who were union members. There were no contributions made to multi-employer pension plans in 2021, 2020 or 2019. 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 $4.0 million recorded as of both December 31, 2021 and 2020.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies
Commitments and Contingencies	13. Commitments and Contingencies 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. We are in a dispute with a customer regarding the outcome of a completed project and also regarding the obligation to perform subcontract work under two executed letters of intent for subsequent projects that we believe are not enforceable. The customer is claiming approximately $12 million in damages related to performance of the original project as well as excess costs to perform the work that was subject to the letters of intent. We are claiming approximately $9 million composed of unpaid amounts under the completed contract as well as costs and inefficiencies that we suffered. We have a lien on the project, and this matter is currently scheduled for arbitration in the second quarter of 2022 with a likely decision in the following months. As of December 31, 2021, we recorded an accrual for this matter based on our analysis of likely outcomes related to this dispute; however, it is possible that the ultimate outcome and associated costs will deviate from our estimates and that, in the event of an unexpectedly adverse outcome, we may experience additional costs and expenses in future periods. 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. Current market conditions for surety markets and bonding capacity are adequate, with acceptable terms and conditions. Historically, approximately 15% to 25% 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, 2021 were as follows: Workers’ Compensation— Employer’s Liability— General Liability— Auto Liability— Employee Medical— each plan Our $150.0 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 $150.0 million of excess loss coverage for each of general liability, employer’s liability and auto liability.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity
Stockholders' Equity	14. 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, 2021, 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. We have outstanding and exercisable stock options 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, 2021, there were 1.9 million shares available for issuance under this plan. The 2017 Plan will expire in May 2027. 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. On December 8, 2020, the Board approved an extension to the program by increasing the shares authorized for repurchase by 0.7 million shares. Since the inception of the repurchase program, the Board has approved 10.3 million shares to be repurchased. As of December 31, 2021, we have repurchased a cumulative total of 9.7 million shares at an average price of $21.69 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 year ended December 31, 2021, we repurchased 0.4 million shares for approximately $27.1 million at an average price of $74.57 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 zero anti-dilutive stock options excluded from the calculation of diluted EPS for the year ended December 31, 2021 and less than 0.1 million anti-dilutive stock options excluded from the calculation of diluted EPS for the years ended December 31, 2020 and 2019. 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, ​ ​ 2021 2020 2019 Common shares outstanding, end of period ​ 36,091 36,188 36,658 ​ Effect of using weighted average common shares outstanding ​ 194 354 196 ​ Shares used in computing earnings per share—basic ​ 36,285 36,542 36,854 ​ Effect of shares issuable under stock option plans based on the treasury stock method ​ 89 123 204 ​ Effect of restricted and contingently issuable shares ​ 76 73 73 ​ Shares used in computing earnings per share—diluted ​ 36,450 36,738 37,131 ​ ​

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Stock-Based Compensation
Stock-Based Compensation	15. 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 Plan, determined and administered by the compensation committee of the Board of Directors. In 2019, the Board of Directors approved a change to the structure of long-term incentive grants to remove stock options, commencing with the March 2019 equity grant. Total stock-based compensation expense was $10.6 million, $6.9 million and $5.9 million for the years ended December 31, 2021, 2020 and 2019, 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 $2.2 million, $1.5 million and $1.3 million for each of the years ended December 31, 2021, 2020 and 2019. 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 Stock options are accounted for as equity instruments. 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. We did not grant any options in 2019, 2020 or 2021. We had no unrecognized compensation cost related to stock options and no unvested stock options as of December 31, 2021. The total fair value of options vested during the year ended December 31, 2021 was $0.4 million. The following table summarizes activity under our stock option plans (shares in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ December 31, 2021 ​ ​ ​ Weighted- ​ ​ ​ ​ ​ Average ​ Stock Options Shares Exercise Price Outstanding at beginning of year 268 ​ $ 30.53 ​ Granted — ​ $ — ​ Exercised (198) ​ $ 28.95 ​ Forfeited — ​ $ — ​ Expired — ​ $ — ​ Outstanding at end of year 70 ​ $ 34.97 ​ Options exercisable at end of year 70 ​ ​ ​ ​ ​ The total intrinsic value of options exercised during the years ended December 31, 2021, 2020 and 2019 was $10.8 million, $3.2 million and $3.5 million, respectively. As of December 31, 2021, we have 0.1 million options outstanding and exercisable; these options have a weighted-average exercise price of $34.97 per share, have a weighted-average remaining contractual term of 5.0 years and an aggregate intrinsic value of $4.5 million. The following table summarizes information about stock options outstanding at December 31, 2021 (shares in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options Outstanding and Exercisable ​ ​ Weighted- ​ ​ ​ ​ Number ​ Average ​ ​ ​ ​ ​ Outstanding and ​ Remaining ​ Weighted- ​ ​ Exercisable at ​ Contractual ​ Average Range of Exercise Prices 12/31/2021 Life (in years) Exercise Price $16.15 - $30.36 28 4.0 ​ $ 28.13 ​ $36.25 - $54.38 42 5.7 ​ $ 39.44 ​ $16.15 - $54.38 70 5.0 ​ $ 34.97 ​ ​ ​ Restricted Stock and Restricted Stock Units The following table summarizes activity under our restricted stock plans (shares in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ December 31, 2021 ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ Average Grant ​ Restricted Stock and Restricted Stock Units Shares Date Fair Value Unvested at beginning of year 120 ​ $ 45.21 ​ Granted 67 ​ $ 76.73 ​ Vested (72) ​ $ 54.53 ​ Forfeited — ​ $ — ​ Unvested at end of year 115 ​ $ 57.74 ​ ​ Approximately $1.5 million of compensation expense related to restricted stock and restricted stock units will be recognized over a weighted-average period of 1.8 years. The total fair value of shares vested during the year ended December 31, 2021 was $3.9 million. The weighted-average fair value per share of restricted stock shares and units awarded during 2021, 2020 and 2019 was $76.73, $39.03 and $51.02, respectively. The aggregate intrinsic value of restricted stock vested during the years ended December 31, 2021, 2020 and 2019 was $5.5 million, $2.9 million and $3.5 million, respectively. Performance Stock Units Under the 2012 Plan and the 2017 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, 2021 was $10.2 million. Of this amount, $3.6 million relates to the PSUs granted in 2019 whose performance period ended December 31, 2021. 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, 2021, 2020 and 2019 was $5.7 million, $2.7 million and $1.9 million, respectively. At the December 31, 2021 calculated fair market value, approximately $1.1 million of compensation expense related to performance stock units will be recognized over a weighted-average period of 1.4 years.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2021
Segment Information
Segment Information	16. Segment Information ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mechanical Services Electrical Services Corporate Consolidated Total Assets at December 31, 2021 ​ $ 1,452,527 ​ $ 690,364 ​ $ 66,223 ​ $ 2,209,114 Total Assets at December 31, 2020 ​ $ 1,246,098 ​ $ 419,475 ​ $ 91,782 ​ $ 1,757,355 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2021 ​ Mechanical Services Electrical Services Corporate Consolidated Revenue ​ $ 2,542,623 ​ $ 531,013 ​ $ — ​ $ 3,073,636 Gross Profit ​ $ 486,346 ​ $ 76,861 ​ $ — ​ $ 563,207 Capital Expenditures ​ $ 19,408 ​ $ 2,413 ​ $ 509 ​ $ 22,330 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2020 ​ Mechanical Services Electrical Services Corporate Consolidated Revenue ​ $ 2,430,632 ​ $ 426,027 ​ $ — ​ $ 2,856,659 Gross Profit ​ $ 513,760 ​ $ 33,223 ​ $ — ​ $ 546,983 Capital Expenditures ​ $ 22,561 ​ $ 944 ​ $ 626 ​ $ 24,131 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2019 ​ Mechanical Services Electrical Services Corporate Consolidated Revenue ​ $ 2,272,031 ​ $ 343,246 ​ $ — ​ $ 2,615,277 Gross Profit ​ $ 469,347 ​ $ 32,596 ​ $ — ​ $ 501,943 Capital Expenditures ​ $ 28,070 ​ $ 1,367 ​ $ 2,313 ​ $ 31,750 ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Estimates (Policies)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies and Estimates
Principles of Consolidation	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 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	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, self-insurance accruals, deferred tax assets, fair value accounting for acquisitions and the quantification of fair value for reporting units in connection with our goodwill impairment testing.
Cash Flow Information	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, ​ 2021 2020 2019 Interest ​ $ 6,052 ​ $ 7,684 ​ $ 8,817 ​ Income taxes, net of refunds ​ $ 52,204 ​ $ 51,286 ​ $ 45,288 ​
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements ​ In December 2019, the FASB issued ASU No. 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes.” This standard simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in Topic 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The standard also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. ASU No. 2019-12 is effective for fiscal years beginning after December 15, 2020 and interim periods within that year. We adopted ASU No. 2019-12 on January 1, 2021, and the impact was not material to our overall financial statements. ​ Recent Accounting Pronouncements Not Yet Adopted ​ In March 2020, the FASB issued ASU No. 2020-04, “Reference Rate Reform (Topic 848).” The pronouncement provides temporary optional expedients and exceptions to the current guidance on contract modifications and hedge accounting to ease the financial reporting burden related to the expected market transition from the London Interbank Offered Rate (“LIBOR”) and other interbank offered rates to alternative reference rates. The guidance was effective upon issuance and generally can be applied to applicable contract modifications through December 31, 2022. Our current debt facility (as further described in Note 9) includes a Eurodollar Rate Loan Option with an interest rate that is determined based on the one- to six-month LIBOR rates, which will cease to be published on June 30, 2023. We are currently evaluating the impact of the transition from LIBOR to alternative reference rates but do not expect a significant impact to our consolidated financial statements. ​ In October 2021, the FASB issued ASU 2021-08, “Business Combinations (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers.” This standard requires an acquirer to apply Accounting Standards Codification Topic 606 to recognize and measure contract assets and contract liabilities in a business combination. ASU 2021-08 is effective for fiscal years beginning after December 15, 2022 and interim periods within that year. Early adoption is permitted. We are currently evaluating the potential impact of this authoritative guidance on our consolidated financial statements. ​
Revenue Recognition	Revenue Recognition 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, for delivery of 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, 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 construction 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. Our revenue recognition policy is further discussed in Note 3 “Revenue from Contracts with Customers.”
Accounts Receivable and Allowance for Credit Losses	Accounts Receivable and Allowance for Credit Losses ​ We are required to estimate and record the expected credit losses over the contractual life of our financial assets measured at amortized cost, including billed and unbilled accounts receivable, other receivables and costs and estimated earnings in excess of billings. Accounts receivable include amounts from work completed in which we have billed or have an unconditional right to bill our customers. Our trade receivables are contractually due in less than a year. ​ We estimate our credit losses using a loss-rate method for each of our identified portfolio segments. Our portfolio segments are construction, service and other. While our construction and service financial assets are often with the same subset of customers and industries, our construction financial assets will generally have a lower loss-rate than service financial assets due to lien rights, which we are more likely to have on construction jobs. These lien rights result in lower credit loss expenses on average compared to receivables that do not have lien rights. Financial assets classified as Other include receivables that are not related to our core revenue producing activities, such as receivables related to our acquisition activity from former owners, our vendor rebate program or receivables for estimated losses in excess of our insurance deductible, which are accrued with a corresponding accrued insurance liability. ​ Loss rates for our portfolios are based on numerous factors, including our history of credit loss expense by portfolio, the financial strength of our customers and counterparties in each portfolio, the aging of our receivables, our expectation of likelihood of payment, macroeconomic trends in the U.S. and the current and forecasted non-residential construction market trends in the U.S. ​ In addition to the loss-rate calculations discussed above, we also record allowance for credit losses for specific receivables that are deemed to have a higher risk profile than the rest of the respective pool of receivables (e.g., when we hold concerns about a specific customer going bankrupt and no longer being able to pay the receivables due to us). ​ Starting in March 2020, we experienced negative impacts to our business due to the disruption caused by Coronavirus Disease 2019 (“COVID-19”). In March 2020, the World Health Organization categorized COVID-19 as a pandemic, and the President of the United States declared the COVID-19 outbreak a national emergency. The Company considered the impact of COVID-19 on the assumptions and estimates used to determine the results reported and asset valuations as of December 31, 2021 and December 31, 2020. ​ In 2020, we increased our loss rates and increased our specific reserves primarily due to the economic disruption caused by COVID-19, which was reflected in our bad debt expense in the prior year. This increase was primarily, but not exclusively, due to concern over collectability of receivables from customers more directly impacted by COVID-19. In 2021, we collected some of these reserve amounts and reduced our assessed risk on collectability as business impacts relating to COVID-19 have stabilized. ​ Activity in our allowance for credit losses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Year Ended December 31, ​ 2021 ​ 2020 ​ Service ​ Construction ​ Other ​ Total ​ Service ​ Construction ​ Other ​ Total Balance at beginning of year $ 4,637 ​ $ 6,028 ​ $ 44 ​ $ 10,709 ​ $ 3,192 ​ $ 3,400 ​ $ 315 ​ $ 6,907 Impact of new accounting standard ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ 310 ​ ​ 331 ​ ​ 54 ​ ​ 695 Bad debt expense (benefit) ​ (970) ​ ​ (496) ​ ​ 14 ​ ​ (1,452) ​ ​ 2,566 ​ ​ 2,697 ​ ​ (10) ​ ​ 5,253 Deductions for uncollectible receivables written off, net of recoveries ​ (742) ​ ​ (244) ​ ​ — ​ ​ (986) ​ ​ (1,431) ​ ​ (735) ​ ​ — ​ ​ (2,166) Credit allowance of acquired receivables on the acquisition date ​ 369 ​ ​ 1,470 ​ ​ — ​ ​ 1,839 ​ ​ — ​ ​ 335 ​ ​ — ​ ​ 335 Reclass to other current liabilities ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ (315) ​ ​ (315) Balance at end of period $ 3,294 ​ $ 6,758 ​ $ 58 ​ $ 10,110 ​ $ 4,637 ​ $ 6,028 ​ $ 44 ​ $ 10,709
Inventories	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 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	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. 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. We perform a goodwill impairment review for each of our operating units, as we have determined that each of our operating units are 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, or if we elect to perform a quantitative assessment, 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 or their useful lives.
Long-Lived Assets	Long-Lived Assets Long-lived assets are comprised principally of identifiable intangible assets, property and equipment, lease right-of-use assets 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 undiscounted cash flows, as well as other economic and business factors, to assess the recoverability of these assets.
Acquisitions	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 Contingent Assets and Liabilities 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	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, such as workers’ compensation, auto liability and general liability, are reviewed by a third-party actuary quarterly. Our self-insurance arrangements are further discussed in Note 13 “Commitments and Contingencies.”
Warranty Costs	Warranty Costs We typically warrant labor for the first year after installation on new MEP systems that we build and install, and we pass through to the customer manufacturers’ warranties on equipment. We generally warrant labor for thirty days after servicing existing MEP 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	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, uncertain tax positions, and accounting for losses associated with underperforming operations. ​ 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. 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 record unrecognized tax benefits as liabilities when, despite our belief that our tax return positions are supportable, we believe that some portion of our uncertain tax positions may be disallowed. When facts and circumstances change, we adjust these liabilities 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 are accrued and classified as a component in the provision for income taxes in our Consolidated Statements of Operations.
Concentrations of Credit Risk	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 related to 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 credit losses. We have a diverse customer base, with our top customer representing 9% of consolidated 2021 revenue.
Financial Instruments	Financial Instruments Our financial instruments consist of cash and cash equivalents, accounts receivable, other receivables, accounts payable, interest rate swaps and life insurance policies, for which we deem the carrying values approximate their fair value due to the short-term nature of these instruments, as well as notes to former owners, a revolving credit facility and a term loan. We believe the carrying value of our debt associated with our senior credit facility approximates its fair value due to the variable rate on such debt.
Insurance Recovery	Insurance Recovery We recorded a $4.8 million gain in the fourth quarter of 2019 due to insurance proceeds we received in the fourth quarter. Approximately $1.6 million of the gain was recorded as a reduction in SG&A, and the remainder was recorded as a reduction in Cost of Services expense. These proceeds related to recoverable costs that were primarily incurred prior to the fourth quarter in 2019.
Leases	We lease certain facilities, vehicles and equipment primarily under noncancelable operating leases. The most significant portion of these noncancelable operating leases are for the facilities occupied by our corporate office and our operating locations. We have finance leases on vehicles that are not material to our consolidated financial position. As of December 31, 2021, the lease liabilities associated with these finance leases ​ The lease terms generally range from three ​ A majority of the Company’s real property leases are with individuals or entities with whom we have no other business relationship. However, in certain instances the Company enters into real property leases with current or former employees. Rent paid to related parties for the years ended December 31, 2021, 2020 and 2019 was approximately $4.9 million, $4.2 million and $3.7 million, respectively. ​ If we decide to cancel or terminate a lease before the end of its term, we would typically owe the lessor the remaining lease payments under the term of the lease. Our lease agreements do not contain any material residual value guarantees or material restrictive covenants. On rare occasions, we rent or sublease certain real estate assets that we no longer use to third parties. ​ Finance lease right-of-use assets are included in “Property and equipment, net,” and current and long-term finance lease liabilities are included within “Current maturities of long-term debt” and “Long-term debt, net,” respectively, in the Consolidated Balance Sheet. The following table summarizes the operating lease assets and liabilities included in the Consolidated Balance Sheet as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 ​ December 31, 2020 Operating lease right-of-use assets $ 124,756 ​ $ 94,727 Operating lease liabilities: ​ ​ ​ ​ ​ Other current liabilities $ 19,050 ​ $ 16,586 Long-term operating lease liabilities ​ 107,701 ​ ​ 80,576 Total operating lease liabilities $ 126,751 ​ $ 97,162 ​ The maturities of operating lease liabilities as of December 31, 2021 are as follows (in thousands): ​ ​ ​ ​ ​ Year ending December 31— ​ ​ ​ 2022 ​ $ 23,729 2023 ​ ​ 21,142 2024 ​ ​ 18,738 2025 ​ ​ 17,642 2026 ​ ​ 14,631 Thereafter ​ ​ 55,161 Total Lease Payments ​ ​ 151,043 Less—Present Value Discount ​ ​ (24,292) Present Value of Operating Lease Liabilities ​ $ 126,751 ​ Supplemental information related to operating leases was as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 ​ 2020 Cash paid for amounts included in the measurement of operating lease liabilities $ 22,232 ​ $ 20,443 Operating lease right-of-use assets obtained in exchange for lease liabilities $ 47,621 ​ $ 27,346

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Estimates (Tables)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies and Estimates
Schedule of cash paid	Cash paid (in thousands) for: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 2019 Interest ​ $ 6,052 ​ $ 7,684 ​ $ 8,817 ​ Income taxes, net of refunds ​ $ 52,204 ​ $ 51,286 ​ $ 45,288 ​
Schedule of activity in allowance for credit losses	Activity in our allowance for credit losses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Year Ended December 31, ​ 2021 ​ 2020 ​ Service ​ Construction ​ Other ​ Total ​ Service ​ Construction ​ Other ​ Total Balance at beginning of year $ 4,637 ​ $ 6,028 ​ $ 44 ​ $ 10,709 ​ $ 3,192 ​ $ 3,400 ​ $ 315 ​ $ 6,907 Impact of new accounting standard ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ 310 ​ ​ 331 ​ ​ 54 ​ ​ 695 Bad debt expense (benefit) ​ (970) ​ ​ (496) ​ ​ 14 ​ ​ (1,452) ​ ​ 2,566 ​ ​ 2,697 ​ ​ (10) ​ ​ 5,253 Deductions for uncollectible receivables written off, net of recoveries ​ (742) ​ ​ (244) ​ ​ — ​ ​ (986) ​ ​ (1,431) ​ ​ (735) ​ ​ — ​ ​ (2,166) Credit allowance of acquired receivables on the acquisition date ​ 369 ​ ​ 1,470 ​ ​ — ​ ​ 1,839 ​ ​ — ​ ​ 335 ​ ​ — ​ ​ 335 Reclass to other current liabilities ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ (315) ​ ​ (315) Balance at end of period $ 3,294 ​ $ 6,758 ​ $ 58 ​ $ 10,110 ​ $ 4,637 ​ $ 6,028 ​ $ 44 ​ $ 10,709

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2021
Revenue from Contract with Customers
Schedule of contracts in progress	Contracts in progress are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 Costs incurred on contracts in progress ​ $ 3,723,715 ​ $ 3,103,580 ​ Estimated earnings, net of losses ​ 589,286 ​ 548,435 ​ Less—Billings to date ​ (4,527,801) ​ (3,813,171) ​ Less—Unbilled accounts receivable ​ ​ (61,881) ​ ​ (45,596) ​ Less—Unbilled accounts receivable credit allowance ​ ​ (715) ​ ​ (784) ​ ​ ​ $ (277,396) ​ $ (207,536) ​ ​ ​ ​ ​ ​ ​ ​ ​ Costs and estimated earnings in excess of billings ​ $ 29,900 ​ $ 18,622 ​ Plus—Costs and estimated earnings in excess of billings credit allowance ​ ​ 84 ​ ​ 79 ​ Billings in excess of costs and estimated earnings ​ (307,380) ​ (226,237) ​ ​ ​ $ (277,396) ​ $ (207,536) ​
Schedule of disaggregation of revenue	Our consolidated 2021 revenue was derived from contracts to provide service activities in the mechanical and electrical services segments we serve. Refer to Note 16 “Segment Information” for additional information on our reportable segments. We disaggregate our revenue from contracts with customers by activity, customer type and service provided, as we believe it best depicts how the nature, amount, timing and uncertainty of our revenue and cash flows are affected by economic factors. See details in the following tables (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Revenue by Service Provided 2021 ​ 2020 ​ ​ 2019 ​ Mechanical Services ​ ​ $ 2,542,623 82.7 % ​ $ 2,430,632 85.1 % ​ $ 2,272,031 ​ 86.9 % Electrical Services ​ ​ ​ 531,013 ​ 17.3 % ​ ​ 426,027 ​ 14.9 % ​ ​ 343,246 ​ 13.1 % Total ​ ​ $ 3,073,636 ​ 100.0 % ​ $ 2,856,659 ​ 100.0 % ​ $ 2,615,277 ​ 100.0 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Revenue by Type of Customer ​ ​ 2021 ​ ​ 2020 ​ 2019 Industrial ​ ​ $ 1,356,688 ​ 44.1 % ​ $ 1,112,075 ​ 38.9 % ​ $ 886,668 ​ 33.9 % Education ​ ​ ​ 390,251 ​ 12.7 % ​ ​ 487,922 ​ 17.1 % ​ ​ 412,318 ​ 15.8 % Office Buildings ​ ​ ​ 308,799 ​ 10.1 % ​ ​ 319,426 ​ 11.2 % ​ ​ 348,640 ​ 13.3 % Healthcare ​ ​ ​ 417,901 ​ 13.6 % ​ ​ 371,105 ​ 13.0 % ​ ​ 358,155 ​ 13.7 % Government ​ ​ ​ 174,813 ​ 5.7 % ​ ​ 163,717 ​ 5.7 % ​ ​ 162,507 ​ 6.2 % Retail, Restaurants and Entertainment ​ ​ ​ 213,386 ​ 6.9 % ​ ​ 239,541 ​ 8.4 % ​ ​ 248,083 ​ 9.5 % Multi-Family and Residential ​ ​ ​ 112,779 ​ 3.7 % ​ ​ 86,799 ​ 3.0 % ​ ​ 104,693 ​ 4.0 % Other ​ ​ ​ 99,019 ​ 3.2 % ​ ​ 76,074 ​ 2.7 % ​ ​ 94,213 ​ 3.6 % Total ​ ​ $ 3,073,636 ​ 100.0 % ​ $ 2,856,659 ​ 100.0 % ​ $ 2,615,277 ​ 100.0 % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ Revenue by Activity Type ​ ​ 2021 ​ ​ 2020 ​ 2019 ​ New Construction ​ ​ $ 1,421,784 ​ 46.3 % ​ $ 1,333,739 ​ 46.7 % ​ $ 1,201,122 ​ 45.9 % Existing Building Construction ​ ​ ​ 963,461 ​ 31.3 % ​ ​ 910,807 ​ 31.9 % ​ ​ 793,159 ​ 30.3 % Service Projects ​ ​ ​ 278,582 ​ 9.1 % ​ ​ 241,402 ​ 8.4 % ​ ​ 231,228 ​ 8.9 % Service Calls, Maintenance and Monitoring ​ ​ ​ 409,809 ​ 13.3 % ​ ​ 370,711 ​ 13.0 % ​ ​ 389,768 ​ 14.9 % Total ​ ​ $ 3,073,636 ​ 100.0 % ​ $ 2,856,659 ​ 100.0 % ​ $ 2,615,277 ​ 100.0 %
Schedule of contract assets and liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ Year Ended December 31, ​ 2021 ​ 2020 ​ Contract Contract ​ Contract Contract ​ Assets ​ Liabilities ​ Assets ​ Liabilities Balance at beginning of period $ 18,622 ​ $ 226,237 ​ $ 2,736 ​ $ 166,918 Change due to acquisitions / disposals ​ 10,356 ​ ​ 36,523 ​ ​ 9,509 ​ ​ 39,885 Change related to credit allowance ​ (5) ​ ​ — ​ ​ (79) ​ ​ — Other changes in the period ​ 927 ​ ​ 44,620 ​ ​ 6,456 ​ ​ 19,434 Balance at end of period $ 29,900 ​ $ 307,380 ​ $ 18,622 $ 226,237

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
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	The following table summarizes the fair values, and levels within the fair value hierarchy in which the fair value measurements are included, for assets and liabilities measured on a recurring basis as of December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2021 ​ Level 1 Level 2 Level 3 Total Cash and cash equivalents ​ $ 58,776 ​ $ — ​ $ — ​ $ 58,776 Life insurance—cash surrender value ​ $ — ​ $ 6,643 ​ $ — ​ $ 6,643 Contingent earn-out obligations ​ $ — ​ $ — ​ $ 34,114 ​ $ 34,114 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2020 ​ Level 1 Level 2 Level 3 Total Cash and cash equivalents ​ $ 54,896 ​ $ — ​ $ — ​ $ 54,896 Life insurance—cash surrender value ​ $ — ​ $ 5,420 ​ $ — ​ $ 5,420 Contingent earn-out obligations ​ $ — ​ $ — ​ $ 25,979 ​ $ 25,979 Interest rate swap liability ​ $ — ​ $ 42 ​ $ — ​ $ 42 ​
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, ​ ​ 2021 2020 Balance at beginning of year $ 25,979 $ 28,497 Issuances ​ 19,949 ​ 16,715 ​ Settlements ​ ​ (3,994) ​ ​ (10,114) ​ Adjustments to fair value ​ (7,820) ​ (9,119) ​ Balance at end of year ​ $ 34,114 ​ $ 25,979 ​

Acquisitions (Tables)

Acquisitions (Tables) - Amteck	12 Months Ended
	Dec. 31, 2021
Business Acquisition [Line Items]
Schedule of acquisition date fair value of consideration transferred and the acquisition date fair value of the identifiable assets acquired and liabilities assumed, including an amount for goodwill	The following summarizes the acquisition date fair value of consideration transferred and the acquisition date fair value of the identifiable assets acquired and liabilities assumed, including an amount for goodwill (in thousands): ​ ​ ​ ​ Consideration transferred: ​ ​ Cash paid at closing $ 107,355 Working capital adjustment ​ 7,409 Notes issued to former owners ​ 10,000 Estimated fair value of contingent earn-out payments ​ 12,900 ​ $ 137,664 Recognized amounts of identifiable assets acquired and liabilities assumed: ​ ​ Cash and cash equivalents $ 13,554 Billed and unbilled accounts receivable ​ 43,248 Other current assets ​ 3,422 Property and equipment ​ 3,886 Goodwill ​ 55,076 Identifiable intangible assets ​ 57,700 Operating lease right-of-use asset ​ 8,997 Accounts payable ​ (14,489) Billings in excess of costs and estimated earnings ​ (15,199) Current maturities of long-term debt ​ (1,860) Current operating lease liabilities ​ (1,115) Accrued expenses and other current liabilities ​ (6,889) Long-term debt ​ (785) Long-term operating lease liabilities ​ (7,882) ​ $ 137,664
Schedule of acquired intangible assets	The acquired intangible assets include the following (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Valuation Method ​ Estimated Useful Life ​ ​ Estimated Fair Value Backlog ​ Excess earnings ​ 1.5 years ​ $ 7,800 Trade Name ​ Relief-from-royalty ​ 23 years ​ ​ 12,600 Customer Relationships ​ Excess earnings ​ 9 years ​ ​ 37,300 Total ​ ​ ​ ​ ​ $ 57,700

Goodwill and Identifiable Int_2

Goodwill and Identifiable Intangible Assets, Net (Tables)	12 Months Ended
	Dec. 31, 2021
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): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mechanical Services ​ Electrical Services ​ ​ ​ Segment Segment ​ Total Balance at December 31, 2019 ​ $ 234,660 ​ $ 97,787 ​ $ 332,447 Acquisitions and purchase price adjustments (See Note 5) ​ 72,788 ​ ​ 59,157 ​ ​ 131,945 Balance at December 31, 2020 ​ ​ 307,448 ​ ​ 156,944 ​ ​ 464,392 Acquisitions and purchase price adjustments (See Note 5) ​ ​ 52,771 ​ ​ 74,951 ​ ​ 127,722 Impact of segment reorganization ​ ​ 1,101 ​ ​ (1,101) ​ ​ — Balance at December 31, 2021 ​ $ 361,320 ​ $ 230,794 ​ $ 592,114
Schedule of components of identifiable intangible assets	Identifiable intangible assets consist of the following (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ December 31, 2021 ​ December 31, 2020 ​ Remaining Useful Lives Gross Book Accumulated Gross Book Accumulated ​ in Years Value Amortization Value Amortization Customer Relationships 7.6 ​ $ 330,572 ​ $ (130,098) ​ $ 255,692 ​ $ (103,919) Backlog 1.1 ​ 32,300 ​ (20,091) ​ 19,800 ​ (12,600) Trade Names 19.6 ​ 114,795 ​ (22,697) ​ 91,495 ​ (18,661) Total ​ ​ ​ $ 477,667 ​ $ (172,886) ​ $ 366,987 ​ $ (135,180) ​
Schedule of future amortization expense of identifiable intangible assets	As of December 31, 2021, future amortization expense of identifiable intangible assets was as follows (in thousands): ​ ​ ​ ​ ​ Year ending December 31— ​ ​ 2022 ​ $ 46,505 ​ 2023 ​ 34,532 ​ 2024 ​ 32,343 ​ 2025 ​ 30,156 ​ 2026 ​ ​ 29,312 ​ Thereafter ​ 131,933 ​ Total ​ $ 304,781 ​

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2021
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 2021 2020 Land — ​ $ 6,792 ​ $ 7,167 ​ Transportation equipment 1 - 7 ​ 132,792 ​ 113,802 ​ Machinery and equipment 1 - 20 ​ 48,000 ​ 43,386 ​ Computer and telephone equipment 1 - 10 ​ 23,065 ​ 23,215 ​ Buildings and leasehold improvements 1 - 40 ​ 74,981 ​ 69,683 ​ Furniture and fixtures 1 - 17 ​ ​ 6,081 ​ ​ 5,861 ​ Construction in progress — ​ 1,668 ​ 1,294 ​ ​ ​ ​ ​ 293,379 ​ 264,408 ​ Less—Accumulated depreciation ​ ​ ​ (164,825) ​ (147,202) ​ Property and equipment, net ​ ​ ​ $ 128,554 ​ $ 117,206 ​

Detail of Other Current Liabi_2

Detail of Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Detail of Other Current Liabilities
Schedule of other current liabilities	Other current liabilities consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 Accrued warranty costs ​ $ 8,969 ​ $ 8,914 ​ Current lease liability ​ ​ 19,050 ​ ​ 16,586 ​ Accrued job losses ​ 8,962 ​ 2,151 ​ Accrued sales and use tax ​ 3,861 ​ 3,731 ​ Deferred revenue ​ 13,734 ​ 4,559 ​ Liabilities due to former owners ​ 27,613 ​ 10,280 ​ Other current liabilities ​ 37,211 ​ 45,271 ​ ​ ​ $ 119,400 ​ $ 91,492 ​

Debt Obligations (Tables)

Debt Obligations (Tables)	12 Months Ended
	Dec. 31, 2021
Debt Obligations
Schedule of components of debt obligations	Debt obligations consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2021 2020 Revolving credit facility ​ $ 220,000 ​ $ 70,000 ​ Term loan ​ ​ 120,000 ​ ​ 135,000 ​ Notes to former owners ​ ​ 47,954 ​ 31,000 ​ Finance lease liabilities (See Note 10) ​ ​ 266 ​ ​ — ​ Total principal amount ​ ​ 388,220 ​ 236,000 ​ Less—unamortized debt issuance costs ​ ​ (190) ​ ​ (267) ​ Total debt, net of unamortized debt issuance costs ​ ​ 388,030 ​ ​ 235,733 ​ Less—current portion ​ ​ (2,788) ​ — ​ Total long-term portion of debt, net ​ $ 385,242 ​ $ 235,733 ​ ​
Schedule of future principal payments of long-term debt	At December 31, 2021, future principal payments of debt are as follows (in thousands): ​ ​ ​ ​ ​ Year ending December 31— ​ ​ 2022 $ 2,788 2023 ​ 27,981 ​ 2024 ​ 35,352 ​ 2025 ​ 322,099 ​ ​ ​ $ 388,220 ​
Schedule of interest expense	Interest expense included the following primary elements (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 2019 Interest expense on notes to former owners ​ $ 1,052 ​ $ 1,354 ​ $ 1,531 ​ Interest expense on borrowings and unused commitment fees ​ 3,371 ​ 5,319 ​ 6,887 ​ Interest expense on interest rate swaps ​ ​ 499 ​ ​ 338 ​ ​ — ​ Interest expense on finance leases ​ ​ 57 ​ ​ — ​ ​ — ​ Letter of credit fees ​ 679 ​ 830 ​ 512 ​ Amortization of debt financing costs ​ 538 ​ 544 ​ 387 ​ Total ​ $ 6,196 ​ $ 8,385 ​ $ 9,317 ​
Schedule of market rates relating to interest options under the Facility	​ ​ ​ ​ Base Rate Loan Option: Federal Funds Rate plus 0.50% 0.57% ​ Wells Fargo Bank, N.A. Prime Rate ​ 3.25% ​ One-month LIBOR plus 1.00% ​ 1.10% ​ Eurodollar Rate Loan Option: ​ ​ ​ One-month LIBOR ​ 0.10% ​ Six-month LIBOR ​ 0.34% ​
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 %

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases
Schedule of operating lease assets and liabilities	Finance lease right-of-use assets are included in “Property and equipment, net,” and current and long-term finance lease liabilities are included within “Current maturities of long-term debt” and “Long-term debt, net,” respectively, in the Consolidated Balance Sheet. The following table summarizes the operating lease assets and liabilities included in the Consolidated Balance Sheet as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 ​ December 31, 2020 Operating lease right-of-use assets $ 124,756 ​ $ 94,727 Operating lease liabilities: ​ ​ ​ ​ ​ Other current liabilities $ 19,050 ​ $ 16,586 Long-term operating lease liabilities ​ 107,701 ​ ​ 80,576 Total operating lease liabilities $ 126,751 ​ $ 97,162
Schedule of maturities of lease liabilities	The maturities of operating lease liabilities as of December 31, 2021 are as follows (in thousands): ​ ​ ​ ​ ​ Year ending December 31— ​ ​ ​ 2022 ​ $ 23,729 2023 ​ ​ 21,142 2024 ​ ​ 18,738 2025 ​ ​ 17,642 2026 ​ ​ 14,631 Thereafter ​ ​ 55,161 Total Lease Payments ​ ​ 151,043 Less—Present Value Discount ​ ​ (24,292) Present Value of Operating Lease Liabilities ​ $ 126,751
Schedule of supplemental information related to leases	Supplemental information related to operating leases was as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 ​ 2020 Cash paid for amounts included in the measurement of operating lease liabilities $ 22,232 ​ $ 20,443 Operating lease right-of-use assets obtained in exchange for lease liabilities $ 47,621 ​ $ 27,346

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
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, ​ 2021 2020 2019 Current tax provision— ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ $ 31,283 ​ $ 36,556 ​ $ 33,281 ​ State ​ 8,741 ​ 12,798 ​ 8,388 ​ Total current ​ 40,024 ​ 49,354 ​ 41,669 ​ Deferred tax provision (benefit)— ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ 6,197 ​ (5,483) ​ (3,750) ​ State ​ 705 ​ (2,470) ​ (501) ​ Total deferred ​ 6,902 ​ (7,953) ​ (4,251) ​ Provision for income taxes ​ $ 46,926 ​ $ 41,401 ​ $ 37,418 ​ ​
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	The provision for income taxes for the years ended December 31, 2021, 2020 and 2019 resulted in effective tax rates on continuing operations of 24.7%, 21.6% and 24.7%, respectively. The reasons for the differences between these effective tax rates and the federal statutory rates are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2021 2020 2019 Federal statutory rate of— ​ ​ 21 % ​ 21 % ​ 21 % Income taxes at the federal statutory rate ​ $ 39,958 ​ $ 40,223 ​ $ 31,866 ​ Increases (decreases) resulting from— ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net state income taxes ​ 7,340 ​ 8,406 ​ 6,644 ​ Valuation allowances ​ (39) ​ (254) ​ (279) ​ Net unrecognized tax benefits ​ 640 ​ 18,557 ​ 7,338 ​ Nondeductible expenses ​ 2,381 ​ 2,470 ​ 2,180 ​ R&D tax credit ​ — ​ (26,133) ​ (4,569) ​ 179D deduction ​ ​ (1,207) ​ ​ (1,062) ​ ​ (5,126) ​ Stock-based compensation deductions ​ ​ (2,210) ​ ​ (426) ​ ​ (714) ​ Other ​ 63 ​ (380) ​ 78 ​ Provision for income taxes ​ $ 46,926 ​ $ 41,401 ​ $ 37,418 ​
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, ​ 2021 2020 Deferred tax assets— ​ ​ ​ ​ ​ ​ ​ Accounts receivable and allowance for credit losses ​ $ 1,878 ​ $ 2,186 ​ Stock-based compensation ​ 3,392 ​ 2,791 ​ Accrued liabilities and expenses ​ 36,255 ​ 39,761 ​ Lease liabilities ​ ​ 27,944 ​ ​ 22,768 ​ Net operating loss carryforwards ​ 10,379 ​ 12,127 ​ Intangible assets ​ ​ 3,851 ​ ​ — ​ Other ​ 758 ​ 627 ​ Subtotal ​ 84,457 ​ 80,260 ​ Valuation allowances ​ (475) ​ (514) ​ Total deferred tax assets ​ ​ 83,982 ​ ​ 79,746 ​ Deferred tax liabilities— ​ ​ ​ ​ ​ ​ ​ Property and equipment ​ (15,534) ​ (13,877) ​ Lease right-of-use asset ​ ​ (27,905) ​ ​ (22,715) ​ Long-term contracts ​ (964) ​ (609) ​ Intangible assets ​ ​ — ​ ​ (242) ​ Goodwill ​ (17,321) ​ (11,615) ​ Other ​ (1,098) ​ (2,626) ​ Total deferred tax liabilities ​ (62,822) ​ (51,684) ​ Net deferred tax assets ​ $ 21,160 ​ $ 28,062 ​
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, ​ 2021 2020 Deferred tax assets ​ $ 22,905 ​ $ 29,401 ​ Deferred tax liabilities ​ $ 1,745 ​ $ 1,339 ​
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, ​ 2021 2020 2019 Balance at beginning of year ​ $ 28,756 ​ $ 10,199 ​ $ 2,966 ​ Additions based on tax positions related to current year ​ 207 ​ — ​ — ​ Additions based on tax positions related to prior years ​ 489 ​ 26,858 ​ 7,473 ​ Reductions for tax positions related to prior years ​ — ​ — ​ (240) ​ Reductions for settlements with tax authorities ​ — ​ (8,301) ​ — ​ Balance at end of year ​ $ 29,452 ​ $ 28,756 ​ $ 10,199 ​

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2021
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, ​ ​ 2021 2020 2019 Common shares outstanding, end of period ​ 36,091 36,188 36,658 ​ Effect of using weighted average common shares outstanding ​ 194 354 196 ​ Shares used in computing earnings per share—basic ​ 36,285 36,542 36,854 ​ Effect of shares issuable under stock option plans based on the treasury stock method ​ 89 123 204 ​ Effect of restricted and contingently issuable shares ​ 76 73 73 ​ Shares used in computing earnings per share—diluted ​ 36,450 36,738 37,131 ​

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 ​ ​ ​ Weighted- ​ ​ ​ ​ ​ Average ​ Stock Options Shares Exercise Price Outstanding at beginning of year 268 ​ $ 30.53 ​ Granted — ​ $ — ​ Exercised (198) ​ $ 28.95 ​ Forfeited — ​ $ — ​ Expired — ​ $ — ​ Outstanding at end of year 70 ​ $ 34.97 ​ Options exercisable at end of year 70 ​ ​ ​ ​
Summary information about stock options outstanding	The following table summarizes information about stock options outstanding at December 31, 2021 (shares in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options Outstanding and Exercisable ​ ​ Weighted- ​ ​ ​ ​ Number ​ Average ​ ​ ​ ​ ​ Outstanding and ​ Remaining ​ Weighted- ​ ​ Exercisable at ​ Contractual ​ Average Range of Exercise Prices 12/31/2021 Life (in years) Exercise Price $16.15 - $30.36 28 4.0 ​ $ 28.13 ​ $36.25 - $54.38 42 5.7 ​ $ 39.44 ​ $16.15 - $54.38 70 5.0 ​ $ 34.97 ​
Restricted Stock
Summary of information about nonvested stock option awards and changes	The following table summarizes activity under our restricted stock plans (shares in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ December 31, 2021 ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ Average Grant ​ Restricted Stock and Restricted Stock Units Shares Date Fair Value Unvested at beginning of year 120 ​ $ 45.21 ​ Granted 67 ​ $ 76.73 ​ Vested (72) ​ $ 54.53 ​ Forfeited — ​ $ — ​ Unvested at end of year 115 ​ $ 57.74 ​

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2021
Segment Information
Summary of information about reportable segments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mechanical Services Electrical Services Corporate Consolidated Total Assets at December 31, 2021 ​ $ 1,452,527 ​ $ 690,364 ​ $ 66,223 ​ $ 2,209,114 Total Assets at December 31, 2020 ​ $ 1,246,098 ​ $ 419,475 ​ $ 91,782 ​ $ 1,757,355 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2021 ​ Mechanical Services Electrical Services Corporate Consolidated Revenue ​ $ 2,542,623 ​ $ 531,013 ​ $ — ​ $ 3,073,636 Gross Profit ​ $ 486,346 ​ $ 76,861 ​ $ — ​ $ 563,207 Capital Expenditures ​ $ 19,408 ​ $ 2,413 ​ $ 509 ​ $ 22,330 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2020 ​ Mechanical Services Electrical Services Corporate Consolidated Revenue ​ $ 2,430,632 ​ $ 426,027 ​ $ — ​ $ 2,856,659 Gross Profit ​ $ 513,760 ​ $ 33,223 ​ $ — ​ $ 546,983 Capital Expenditures ​ $ 22,561 ​ $ 944 ​ $ 626 ​ $ 24,131 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, 2019 ​ Mechanical Services Electrical Services Corporate Consolidated Revenue ​ $ 2,272,031 ​ $ 343,246 ​ $ — ​ $ 2,615,277 Gross Profit ​ $ 469,347 ​ $ 32,596 ​ $ — ​ $ 501,943 Capital Expenditures ​ $ 28,070 ​ $ 1,367 ​ $ 2,313 ​ $ 31,750

Business and Organization (Deta

Business and Organization (Details)	12 Months Ended
	Dec. 31, 2021
Installation of systems in newly constructed facilities
Business and Organization
Percentage of revenue attributable to services	46.30%
Maintenance, repair and replacement services
Business and Organization
Percentage of revenue attributable to services	53.70%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Estimates - Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash paid for:
Interest	$ 6,052	$ 7,684	$ 8,817
Income taxes	$ 52,204	$ 51,286	$ 45,288

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Estimates - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	$ 10,709	$ 6,907
Impact of new accounting standard		695
Bad debt expense (benefit)	(1,452)	5,253	$ 2,978
Deductions for uncollectible receivables written off, net of recoveries	(986)	(2,166)
Credit allowance of acquired receivables on the acquisition date	1,839	335
Reclass to other current liabilities		(315)
Balance at end of year	10,110	10,709	6,907
Service
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	4,637	3,192
Impact of new accounting standard		310
Bad debt expense (benefit)	(970)	2,566
Deductions for uncollectible receivables written off, net of recoveries	(742)	(1,431)
Credit allowance of acquired receivables on the acquisition date	369
Balance at end of year	3,294	4,637	3,192
Construction
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	6,028	3,400
Impact of new accounting standard		331
Bad debt expense (benefit)	(496)	2,697
Deductions for uncollectible receivables written off, net of recoveries	(244)	(735)
Credit allowance of acquired receivables on the acquisition date	1,470	335
Balance at end of year	6,758	6,028	3,400
Other.
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	44	315
Impact of new accounting standard		54
Bad debt expense (benefit)	14	(10)
Reclass to other current liabilities		(315)
Balance at end of year	$ 58	$ 44	$ 315

Summary of Significant Accoun_6

Summary of Significant Accounting Policies and Estimates - Risk (Details)	12 Months Ended
	Dec. 31, 2021
Warranty Costs
Labor warranty period after servicing of existing MEP system	30 days
Revenue | Customer concentration | Minimum
Warranty Costs
Single customer, percentage of revenue	9.00%

Summary of Significant Accoun_7

Summary of Significant Accounting Policies and Estimates - Insurance Recovery (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019USD ($)
Summary of Significant Accounting Policies and Estimates
Gain due to insurance proceeds received	$ 4.8
Gain recorded as reduction in SG&A	1.6
Gain recorded as reduction in cost of services expense	$ 3.2

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Revenue Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Contracts in progress
Costs incurred on contracts in progress	$ 3,723,715	$ 3,103,580
Estimated earnings, net of losses	589,286	548,435
Less-Billings to date	(4,527,801)	(3,813,171)
Less-Unbilled accounts receivable	(61,881)	(45,596)
Less-Unbilled accounts receivable credit allowance	(715)	(784)
Contracts in progress	(277,396)	(207,536)
Costs and estimated earnings in excess of billings	29,900	18,622	$ 2,736
Plus-Costs and estimated earnings in excess of billings credit allowance	84	79
Billings in excess of costs and estimated earnings	$ (307,380)	(226,237)	$ (166,918)
Period during which progress billings or contract price can be withheld until completion of work	6 months
Retention receivable	$ 139,500	124,100
Retention payable	$ 24,000	$ 22,200
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
Minimum
Contracts in progress
Receivable payment terms (in days)	45 days
Payments received term (in days)	30 days
Maximum
Contracts in progress
Receivable payment terms (in days)	60 days
Payments received term (in days)	90 days

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue
Revenue	$ 3,073,636	$ 2,856,659	$ 2,615,277
Percentage of revenue from contract with customer (as a percent)	100.00%	100.00%	100.00%
Industrial
Disaggregation of Revenue
Revenue	$ 1,356,688	$ 1,112,075	$ 886,668
Percentage of revenue from contract with customer (as a percent)	44.10%	38.90%	33.90%
Education
Disaggregation of Revenue
Revenue	$ 390,251	$ 487,922	$ 412,318
Percentage of revenue from contract with customer (as a percent)	12.70%	17.10%	15.80%
Office Buildings
Disaggregation of Revenue
Revenue	$ 308,799	$ 319,426	$ 348,640
Percentage of revenue from contract with customer (as a percent)	10.10%	11.20%	13.30%
Healthcare
Disaggregation of Revenue
Revenue	$ 417,901	$ 371,105	$ 358,155
Percentage of revenue from contract with customer (as a percent)	13.60%	13.00%	13.70%
Government
Disaggregation of Revenue
Revenue	$ 174,813	$ 163,717	$ 162,507
Percentage of revenue from contract with customer (as a percent)	5.70%	5.70%	6.20%
Retail, Restaurants and Entertainment
Disaggregation of Revenue
Revenue	$ 213,386	$ 239,541	$ 248,083
Percentage of revenue from contract with customer (as a percent)	6.90%	8.40%	9.50%
Multi-Family and Residential
Disaggregation of Revenue
Revenue	$ 112,779	$ 86,799	$ 104,693
Percentage of revenue from contract with customer (as a percent)	3.70%	3.00%	4.00%
Other
Disaggregation of Revenue
Revenue	$ 99,019	$ 76,074	$ 94,213
Percentage of revenue from contract with customer (as a percent)	3.20%	2.70%	3.60%
New Construction
Disaggregation of Revenue
Revenue	$ 1,421,784	$ 1,333,739	$ 1,201,122
Percentage of revenue from contract with customer (as a percent)	46.30%	46.70%	45.90%
Existing Building Construction
Disaggregation of Revenue
Revenue	$ 963,461	$ 910,807	$ 793,159
Percentage of revenue from contract with customer (as a percent)	31.30%	31.90%	30.30%
Service Projects
Disaggregation of Revenue
Revenue	$ 278,582	$ 241,402	$ 231,228
Percentage of revenue from contract with customer (as a percent)	9.10%	8.40%	8.90%
Service Calls, Maintenance and Monitoring
Disaggregation of Revenue
Revenue	$ 409,809	$ 370,711	$ 389,768
Percentage of revenue from contract with customer (as a percent)	13.30%	13.00%	14.90%
Mechanical Services
Disaggregation of Revenue
Revenue	$ 2,542,623	$ 2,430,632	$ 2,272,031
Percentage of revenue from contract with customer (as a percent)	82.70%	85.10%	86.90%
Electrical Services
Disaggregation of Revenue
Revenue	$ 531,013	$ 426,027	$ 343,246
Percentage of revenue from contract with customer (as a percent)	17.30%	14.90%	13.10%

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Contract Assets
Balance at beginning of period	$ 18,622	$ 2,736
Change due to acquisitions / disposals	10,356	9,509
Change related to credit allowance	(5)	(79)
Other changes in the period	927	6,456
Balance at end of period	29,900	18,622
Contract Liabilities
Balance at beginning of period	226,237	166,918
Change due to acquisitions / disposals	36,523	39,885
Other changes in the period	44,620	19,434
Balance at end of period	307,380	226,237
Revenue related to our contract liabilities	$ 207,600
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Contract Liabilities
Revenue related to our contract liabilities		$ 165,800

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Remaining Performance Obligations (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Remaining Performance Obligations
The term of the renewable service maintenance agreements (in years)	1 year
Practical Expedient	true
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Remaining Performance Obligations
Remaining performance obligations	$ 2,310
Expected timing of performance obligations	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Minimum
Remaining Performance Obligations
Expected percentage of remaining performance obligations	80.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Maximum
Remaining Performance Obligations
Expected percentage of remaining performance obligations	85.00%

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)item	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Fair Value Measurements
Number of employees covered under life insurance policies | item	85
Combined face value of life insurance policies	$ 62,300
Cash surrender value	6,600	$ 5,400
Reconciliation of the fair value of contingent earn-out obligations that use significant unobservable inputs (Level 3)
Impairment charges	$ 0	0	$ 0
Minimum
Fair Value Measurements
Weighted average cost of capital	10.00%
Maximum
Fair Value Measurements
Weighted average cost of capital	16.50%
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	$ 25,979	28,497
Issuances	19,949	16,715
Settlements	(3,994)	(10,114)
Adjustments to fair value	7,820	9,119
Balance at end of period	34,114	25,979	28,497
Recurring basis | Total
Fair Value Measurements
Cash and cash equivalents	58,776	54,896
Life insurance-cash surrender value	6,643	5,420
Contingent earn-out obligations	34,114	25,979
Recurring basis | Quoted Market Prices In Active Markets for Identical Assets (Level 1)
Fair Value Measurements
Cash and cash equivalents	58,776	54,896
Recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value Measurements
Life insurance-cash surrender value	6,643	5,420
Recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Contingent earn-out obligations	34,114	25,979
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)
Impairment charges	0	0	$ 0
Interest Rate Swap
Fair Value Measurements
Net loss on derivative	500	300
Interest Rate Swap | Not Designated as Hedging Instrument, Economic Hedge [Member]
Fair Value Measurements
Notional amount	$ 80,000
Interest Rate Swap | Recurring basis | Total | Not Designated as Hedging Instrument, Economic Hedge [Member]
Fair Value Measurements
Interest rate swap liability		42
Interest Rate Swap | Recurring basis | Significant Other Observable Inputs (Level 2) | Not Designated as Hedging Instrument, Economic Hedge [Member]
Fair Value Measurements
Interest rate swap liability		$ 42

Acquisitions (Details)

Acquisitions (Details) - USD ($) $ in Thousands	Aug. 01, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill		$ 592,114	$ 464,392	$ 332,447
Amteck
Consideration transferred:
Cash paid at closing	$ 107,355
Working capital adjustment	7,409
Notes issued to former owners	10,000
Estimated fair value of contingent earn-out payments	12,900
Total consideration transferred	137,664
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents	13,554
Billed and unbilled accounts receivable	43,248
Other current assets	3,422
Property and equipment	3,886
Goodwill	55,076
Identifiable intangible assets	57,700
Operating lease right-of-use asset	8,997
Accounts payable	(14,489)
Billings in excess of costs and estimated earnings	(15,199)
Current maturities of long-term debt	(1,860)
Current operating lease liabilities	(1,115)
Accrued expenses and other current liabilities	(6,889)
Long-term operating lease liabilities	(785)
Other long-term liabilities	(7,882)
Total assets acquired and liabilities assumed	$ 137,664

Acquisitions - Acquired Intangi

Acquisitions - Acquired Intangible Assets (Details) - Amteck $ in Thousands	Aug. 01, 2021USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value	$ 57,700
Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	1 year 6 months
Estimated Fair Value	$ 7,800
Trade Name
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	23 years
Estimated Fair Value	$ 12,600
Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	9 years
Estimated Fair Value	$ 37,300

Acquisitions - Contingent Earn-

Acquisitions - Contingent Earn-out Obligation (Details) - USD ($) $ in Thousands	Aug. 01, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Revenues			$ 3,073,636	$ 2,856,659	$ 2,615,277
Federal
Business Acquisition [Line Items]
Net operating loss carryforwards		$ 34,200	34,200
State
Business Acquisition [Line Items]
Net operating loss carryforwards		61,700	$ 61,700
Amteck
Business Acquisition [Line Items]
Number of milestones	four
Revenues		$ 83,500
Contingent earn-out period	53 months
Amteck | Minimum
Business Acquisition [Line Items]
Contingent earn-out estimated milestone payment, minimum	$ 100
Cash flow discount rate	14.80%
Amteck | Minimum | Measurement Input, Inception Discount Rate [Member]
Business Acquisition [Line Items]
Cash flow discount rate	14.00%
Amteck | Maximum
Business Acquisition [Line Items]
Contingent earn-out estimated milestone payment, maximum	$ 11,400
Cash flow discount rate	15.20%
Amteck | Maximum | Measurement Input, Inception Discount Rate [Member]
Business Acquisition [Line Items]
Cash flow discount rate	18.50%

Acquisitions - Other Acquisitio

Acquisitions - Other Acquisitions (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 01, 2021	Apr. 01, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
MEP Holdings
Acquisitions
Total purchase price	$ 57.3
Purchase price paid in cash	45.2
Promissory note payable	7.6
Mechanical Contractor Kentucky
Acquisitions
Total purchase price	21.1
Mechanical Contractor Indiana
Acquisitions
Total purchase price	$ 4.6
Ivey
Acquisitions
Total purchase price		$ 78.8
Purchase price paid in cash		64.1
Promissory note payable		8
Other amount payable		$ 0.4
TAS Energy
Acquisitions
Total purchase price			$ 169.5
Purchase price allocated to goodwill and identifiable intangible assets			126.2
Purchase price paid in cash			105.9
Working capital adjustment			40.5
Promissory note payable			14
Contingent earn-out obligation			$ 9.1
TEC
Acquisitions
Total purchase price					$ 88.9
Purchase price paid in cash					73
Working capital adjustment					1.3
Promissory note payable					7
Contingent earn-out obligation					$ 7.6
Electrical Contractor North Carolina
Acquisitions
Total purchase price						$ 41.6
Mechanical Contractor Utah
Acquisitions
Total purchase price				$ 18.1

Goodwill and Identifiable Int_3

Goodwill and Identifiable Intangible Assets, Net - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Changes in the carrying amount of goodwill
Balance at beginning of year	$ 464,392	$ 332,447
Acquisitions and purchase price adjustments (See Note 5)	127,722	131,945
Balance at end of period	592,114	464,392
Mechanical Services Segment
Changes in the carrying amount of goodwill
Balance at beginning of year	307,448	234,660
Acquisitions and purchase price adjustments (See Note 5)	52,771	72,788
Impact of segment reorganization	1,101
Balance at end of period	361,320	307,448
Accumulated impairment charges	116,600	116,600
Electrical Services Industry
Changes in the carrying amount of goodwill
Balance at beginning of year	156,944	97,787
Acquisitions and purchase price adjustments (See Note 5)	74,951	59,157
Impact of segment reorganization	(1,101)
Balance at end of period	$ 230,794	$ 156,944

Goodwill and Identifiable Int_4

Goodwill and Identifiable Intangible Assets, Net - Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Identifiable Intangible Assets, Net
Gross Book Value	$ 477,667	$ 366,987
Accumulated Amortization	(172,886)	(135,180)
Future amortization expense of identifiable intangible assets
2022	46,505
2023	34,532
2024	32,343
2025	30,156
2026	29,312
Thereafter	131,933
Total	$ 304,781
Customer Relationships
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	7 years 7 months 6 days
Gross Book Value	$ 330,572	255,692
Accumulated Amortization	$ (130,098)	(103,919)
Customer Relationships | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	7 years 7 months 6 days
Backlog
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year 1 month 6 days
Gross Book Value	$ 32,300	19,800
Accumulated Amortization	$ (20,091)	(12,600)
Backlog | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	1 year 1 month 6 days
Trade Name
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	19 years 7 months 6 days
Gross Book Value	$ 114,795	91,495
Accumulated Amortization	$ (22,697)	$ (18,661)
Trade Name | Minimum
Identifiable Intangible Assets, Net
Estimated Useful Lives in Years	19 years 7 months 6 days
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

Goodwill and Identifiable Int_5

Goodwill and Identifiable Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Asset Impairment Charges [Abstract]
Impairment charges	$ 0	$ 0	$ 0
Amortization of identifiable intangible assets	40,505	32,698	27,082
Goodwill	$ 592,114	$ 464,392	$ 332,447
Walker
Asset Impairment Charges [Abstract]
Fair values in excess of carrying value (as a percent)	32.00%
Goodwill	$ 96,800

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property and equipment
Property and equipment, gross	$ 293,379	$ 264,408
Less-Accumulated depreciation	(164,825)	(147,202)
Property and equipment, net	128,554	117,206
Depreciation expense	28,400	27,900	$ 24,500
Land
Property and equipment
Property and equipment, gross	6,792	7,167
Transportation equipment
Property and equipment
Property and equipment, gross	$ 132,792	113,802
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	$ 48,000	43,386
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	$ 23,065	23,215
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	$ 74,981	69,683
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	$ 6,081	5,861
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	$ 1,668	$ 1,294

Detail of Other Current Liabi_3

Detail of Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Other current liabilities
Accrued warranty costs	$ 8,969	$ 8,914
Current lease liability	19,050	16,586
Operating lease liability	126,751	97,162
Accrued job losses	8,962	2,151
Accrued sales and use tax	3,861	3,731
Deferred revenue	13,734	4,559
Liabilities due to former owners	27,613	10,280
Other current liabilities	37,211	45,271
Total other current liabilities	$ 119,400	$ 91,492

Debt Obligations (Details)

Debt Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Obligations
Finance lease liabilities (See Note 10)	$ 266
Total principal amount	388,220	$ 236,000
Less-unamortized debt issuance costs	(190)	(267)
Total debt, net of unamortized debt issuance costs	388,030	235,733
Less-current portion	2,788
Total long-term portion of debt, net	385,242	235,733
Revolving credit facility
Debt Obligations
Total principal amount	220,000	70,000
Term loan
Debt Obligations
Total principal amount	120,000	135,000
Notes to former owners
Debt Obligations
Outstanding balance	$ 47,954	$ 31,000

Debt Obligations - Future Payme

Debt Obligations - Future Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Future principal payments of long-term debt
2022	$ 2,788
2023	27,981
2024	35,352
2025	322,099
Total debt	388,220
Interest expense
Interest expense on notes to former owners	1,052	$ 1,354	$ 1,531
Interest expense on borrowings and unused commitment fees	3,371	5,319	6,887
Interest expense on interest rate swaps	499	338
Interest expense on finance leases	57
Letter of credit fees	679	830	512
Amortization of debt financing costs	538	544	387
Total	$ 6,196	$ 8,385	$ 9,317

Debt Obligations - Other (Detai

Debt Obligations - Other (Details) $ in Thousands	Dec. 31, 2019USD ($)	Dec. 20, 2019USD ($)	Dec. 19, 2019	Dec. 31, 2021USD ($)item	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Debt Obligations
Payments on term loan				$ 15,000	$ 15,000
Financing and professional cost						$ 1,405
Outstanding balance				388,220	236,000
Reconciliation of Credit Facility Adjusted EBITDA to net income
Net income				143,348	150,139	114,324
Provision for income taxes				46,926	41,401	37,418
Depreciation and amortization expense				(28,400)	(27,900)	(24,500)
Stock-based compensation				$ 10,593	6,934	$ 5,878
Principal financial covenants
Fixed charge coverage ratio				2
Other disclosures
2023				$ 27,981
2024				35,352
Revolving credit facility
Debt Obligations
Borrowing capacity		$ 450,000
Outstanding borrowings				220,000
Outstanding balance				220,000	70,000
Letters of credit amount outstanding				53,500
Credit available				176,500
Book value of assets pledged as collateral				$ 98,900
Number of quarters of net earnings used for the calculation of the credit facility adjusted EBITDA | item				4
Principal financial covenants
Number of interest rate options | item				2
Leverage ratio				1.2
Fixed charge coverage ratio				42
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Weighted average interest rate (as a percent)				1.40%
Revolving credit facility | Through maturity
Principal financial covenants
Leverage ratio				3
Revolving credit facility | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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				1.50
Revolving credit facility | Minimum | Covenant Requirement
Principal financial covenants
Net leverage ratio used as basis for other restrictions				2.50
Revolving credit facility | Maximum
Principal financial covenants
Permitted amount of acquisitions per transaction				$ 5,000
Aggregate purchase price of current acquisition and acquisitions in the preceding 12 month period for determining permitted amount of acquisition per transaction				$ 10,000
Revolving credit facility | Base rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)				2.00%
Amended senior revolving credit facility
Debt Obligations
Borrowing capacity		600,000		$ 570,000
Line of credit borrowing capacity accordion option		150,000
Payments on term loan				30,000
Financing and professional cost	$ 1,400
Term loan
Debt Obligations
Borrowing capacity		$ 150,000
Repayment in terms of percentage of original aggregate principal amount		3.75%	1.25%
Payments of financing costs term loan	$ 400
Outstanding balance				$ 120,000	135,000
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Weighted average interest rate (as a percent)				1.40%
Notes to former owners
Other disclosures
Cumulative number of companies acquired | item				10
Outstanding balance				$ 47,954	$ 31,000
Promissory note | MEP Holdings
Other disclosures
Outstanding balance				$ 7,600
Stated interest rate (as a percent)				2.50%
Promissory note | Ivey
Other disclosures
Outstanding balance				$ 8,000
Stated interest rate (as a percent)				2.50%
Promissory note | Walker
Other disclosures
Outstanding balance				$ 2,000
Stated interest rate (as a percent)				4.00%
Promissory note | Amteck
Other disclosures
Outstanding balance				$ 10,000
Stated interest rate (as a percent)				2.50%
Promissory note | Immaterial acquisitions
Other disclosures
Outstanding balance				$ 20,400
Promissory note | Minimum | Immaterial acquisitions
Other disclosures
Stated interest rate (as a percent)				2.30%
Promissory note | Maximum | Immaterial acquisitions
Other disclosures
Stated interest rate (as a percent)				3.50%
Letter of Credit
Debt Obligations
Borrowing capacity		$ 160,000
Outstanding notes | Immaterial acquisitions
Other disclosures
Number of acquisitions | item				6
Federal Funds Rate | Revolving credit facility | Base rate
Market rates relating to interest options
Market rate (as a percent)				0.57%
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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)				3.25%
One-month LIBOR | Revolving credit facility | Base rate
Market rates relating to interest options
Market rate (as a percent)				1.10%
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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)				0.10%
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)				0.34%

Leases (Details)

Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)Option	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Finance lease liability	$ 266
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	us-gaap:OtherLiabilities
Variable lease expense and short-term lease expenses	$ 11,900	$ 7,700	$ 8,400
Weighted average discount rate for operating leases	4.00%	4.20%
Operating lease expense	$ 34,200	$ 28,200	24,800
Weighted average remaining lease term	8 years 8 months 12 days	7 years 6 months
Rent paid to related parties	$ 4,900	$ 4,200	$ 3,700
Existence of option to extend	true
Minimum
Lessee, Lease, Description [Line Items]
Lease term for operating lease	3 years
Number of options to renew | Option	1
Maximum
Lessee, Lease, Description [Line Items]
Lease term for operating lease	10 years

Leases - Summary of Operating L

Leases - Summary of Operating Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Summary of lease asset and liabilities
Operating lease right-of-use assets	$ 124,756	$ 94,727
Operating lease liabilities:
Other current liabilities	$ 19,050	$ 16,586
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current	Other Liabilities, Current
Long-term operating lease liabilities	$ 107,701	$ 80,576
Total operating lease liabilities	$ 126,751	$ 97,162

Leases - Maturities of Lease Li

Leases - Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Maturities of lease liabilities:
2022	$ 23,729
2023	21,142
2024	18,738
2025	17,642
2026	14,631
Thereafter	55,161
Total Lease Payments	151,043
Less-Present Value Discount	(24,292)
Present Value of Lease Liabilities	126,751	$ 97,162
Supplemental information related to leases:
Cash paid for amounts included in the measurement of lease liabilities	22,232	20,443
Operating lease right-of-use assets obtained in exchange for lease liabilities	$ 47,621	$ 27,346

Income Taxes - Provision (Detai

Income Taxes - Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current tax provision-
Federal	$ 31,283	$ 36,556	$ 33,281
State and Puerto Rico	8,741	12,798	8,388
Total current	40,024	49,354	41,669
Deferred tax provision (benefit)-
Federal	6,197	(5,483)	(3,750)
State and Puerto Rico	705	(2,470)	(501)
Total deferred	6,902	(7,953)	(4,251)
Provision for income taxes	$ 46,926	$ 41,401	$ 37,418

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Sep. 30, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective tax rates on continuing operations			24.70%	21.60%	24.70%
Federal statutory income tax rate (as a percent)			21.00%	21.00%	21.00%
Income taxes at the federal statutory rate			$ 39,958	$ 40,223	$ 31,866
Increases (decreases) resulting from-
Net state income taxes			7,340	8,406	6,644
Valuation allowances			(39)	(254)	(279)
Net unrecognized tax benefits			640	18,557	7,338
Nondeductible expenses			2,381	2,470	2,180
R&D tax credits		$ (4,600)		(26,133)	(4,569)	$ (2,700)
179D deduction			(1,207)	(1,062)	(5,126)
Stock-based compensation deductions			(2,210)	(426)	(714)
Other			63	(380)	78
Provision for income taxes			$ 46,926	$ 41,401	37,418
179D deduction					$ (2,200)
Forecast
Increases (decreases) resulting from-
Interest on income tax refund	$ 1,600

Income Taxes - Provision Change

Income Taxes - Provision Changes, Examination (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Oct. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
R&D tax credits			$ 4,600		$ 26,133	$ 4,569	$ 2,700
Additions based on tax positions related to prior years		$ 7,300		$ 489	26,858	7,473
179D deduction						2,200
Reduced provision for income taxes		8,300			8,301
Provision for income taxes				$ 46,926	$ 41,401	$ 37,418
Internal Revenue Service (IRS)
Income Taxes
Refund claims allowed in Income tax examination		$ 8,900
Total Tax Years 2016-2018
Income Taxes
Additions based on tax positions related to prior years	$ 28,800
R&D Tax Credit and 179D Deduction | Tax Year 2016
Income Taxes
Provision for income taxes	9,800
R&D Tax Credit and 179D Deduction | Tax Year 2017
Income Taxes
Provision for income taxes	9,500
R&D Tax Credit and 179D Deduction | Tax Year 2018
Income Taxes
Provision for income taxes	11,900
R&D Tax Credit and 179D Deduction | Total Tax Years 2016-2018
Income Taxes
Provision for income taxes	$ 31,200

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets-
Accounts receivable and allowance for doubtful accounts	$ 1,878	$ 2,186
Stock-based compensation	3,392	2,791
Accrued liabilities and expenses	36,255	39,761
Lease liabilities	27,944	22,768
Net operating loss carryforwards	10,379	12,127
Intangible assets	3,851
Other	758	627
Subtotal	84,457	80,260
Valuation allowances	(475)	(514)
Total deferred tax assets	83,982	79,746
Property and equipment	(15,534)	(13,877)
Deferred tax liabilities	1,745	1,339
Lease right-of-use asset	(27,905)	(22,715)
Long-term contracts	(964)	(609)
Intangible assets		(242)
Goodwill	(17,321)	(11,615)
Other	(1,098)	(2,626)
Total deferred tax liabilities	(62,822)	(51,684)
Net deferred tax assets	21,160	28,062
Deferred income tax assets
Deferred tax assets	$ 22,905	$ 29,401

Income Taxes - Loss Carryforwar

Income Taxes - Loss Carryforwards and Other (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2022
Operating loss carryforwards
Federal deferred tax assets net operating loss carryforwards		$ 7,200
State deferred tax assets net operating loss carryforwards		3,200
Net deferred tax assets		83,982	$ 79,746
Reconciliation of the beginning and ending amount of unrecognized tax benefits, excluding accrued interest and penalties
Balance at beginning of year		28,756	10,199	$ 2,966
Additions based on tax positions related to current year		207
Additions based on tax positions related to prior years	$ 7,300	489	26,858	7,473
Reductions for tax positions related to prior years				(240)
Reductions for settlements with tax authorities	(8,300)		(8,301)
Balance at end of year		29,452	28,756	10,199
Interest and penalties accrued		0	0	0
Reduced provision for income taxes	$ 8,300		$ 8,301
Decrease in unrecognized tax benefits					$ 28,800
Federal
Operating loss carryforwards
Net operating loss carryforwards		34,200
State
Operating loss carryforwards
Net operating loss carryforwards		61,700
Increase in valuation allowance		400
Net deferred tax assets		$ 2,800

Employee Benefit Plans (Details

Employee Benefit Plans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)item	Dec. 31, 2020USD ($)item	Dec. 31, 2019USD ($)
Employee Benefit Plans
Percentage of contributions of covered employees' salaries or wages	2.50%
Contribution	$ 16.1	$ 16.3	$ 14.2
Amount payable to plan	$ 0.6	$ 0.5
Number of employees who are union members | item	5	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	$ 4

Commitments and Contingencies -

Commitments and Contingencies - Other and Bonds (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)item
Obligation to perform subcontract work | Pending Litigation
Commitments and Contingencies
Letter of intent under dispute | item	2
Damages stated	$ 9
Obligation to perform subcontract work | Customer | Pending Litigation
Commitments and Contingencies
Damages claimed	$ 12
Surety | Minimum
Surety
Percentage of business which has required bonds	15.00%
Surety | Maximum
Surety
Percentage of business which has required bonds	25.00%

Commitments and Contingencies_2

Commitments and Contingencies - Self-Insurance (Details)	Dec. 31, 2021USD ($)item
Self-Insurance
Amount of loss fully insured above per-incident deductible amount	$ 150,000,000
Amount of excess loss insurance covered	150,000,000
Workers Compensation
Self-Insurance
Per incident deductible amount	250,000
Amount of loss fully insured above per-incident deductible amount	250,000
Employer's Liability
Self-Insurance
Per incident deductible amount	250,000
Employer's Liability | Maximum
Self-Insurance
Amount of excess loss insurance covered	150,000,000
General Liability
Self-Insurance
Per incident deductible amount	250,000
Amount of loss fully insured above per-incident deductible amount	10,000,000
General Liability | Maximum
Self-Insurance
Amount of excess loss insurance covered	150,000,000
Auto Liability
Self-Insurance
Per incident deductible amount	250,000
Amount of loss fully insured above per-incident deductible amount	10,000,000
Auto Liability | Maximum
Self-Insurance
Amount of excess loss insurance covered	$ 150,000,000
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 - Incentiv

Stockholders' Equity - Incentive and Other (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	12 Months Ended			177 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021	Dec. 08, 2020	May 31, 2017	May 31, 2012	Mar. 29, 2007
Share Repurchase Program
Share repurchase	$ 27,054	$ 30,120	$ 19,550
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	1.9			1.9
Stock Repurchase Program 2007
Share Repurchase Program
Number of shares of outstanding common stock authorized to be acquired under a stock repurchase program	10.3			10.3				1
Additional number of shares authorized for repurchase					0.7
Share repurchase (in shares)				9.7
Average price (in dollars per share)	$ 74.57			$ 21.69
Share repurchase	$ 27,100
Maximum | Stock Repurchase Program 2007
Share Repurchase Program
Share repurchase (in shares)	0.4

Stockholders' Equity - Anti-Dil

Stockholders' Equity - Anti-Dilutive Stock Options (Details) - Stock Options - shares shares in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share
Anti-dilutive securities excluded from computation of earnings per share amount (in shares)	0
Maximum
Earnings Per Share
Anti-dilutive securities excluded from computation of earnings per share amount (in shares)		0.1	0.1

Stockholders' Equity - Number o

Stockholders' Equity - Number of Shares (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
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	36,091	36,188	36,658
Effect of using weighted average common shares outstanding	194	354	196
Shares used in computing earnings per share-basic	36,285	36,542	36,854
Effect of shares issuable under stock option plans based on the treasury stock method	89	123	204
Effect of restricted and contingently issuable shares	76	73	73
Shares used in computing earnings per share-diluted	36,450	36,738	37,131

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-Based Compensation
Stock-based compensation expense	$ 10.6	$ 6.9	$ 5.9
Income tax benefit	$ 2.2	$ 1.5	1.3
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)	268,000
Exercised (in shares)	(198,000)
Outstanding at end of year (in shares)	70,000	268,000
Options exercisable at end of year (in shares)	70,000
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 30.53
Exercised (in dollars per share)	28.95
Outstanding at end of year (in dollars per share)	$ 34.97	$ 30.53
Other information
Intrinsic value of options exercised	$ 10.8	$ 3.2	$ 3.5
Weighted-average remaining contractual term of options exercisable	5 years
Aggregate intrinsic value of options exercisable	$ 4.5
Number of options that are vested and expected to vest (in shares)	100,000
Weighted average exercise price of options that are vested and expected to vest (in dollars per share)	$ 34.97
Unrecognized compensation cost	$ 0
Nonvested at end of year (in shares)	0

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Option Plan Activity (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2021$ / sharesshares
$16.15 - $30.36
Stock-Based Compensation
Exercise price, low end of range (in dollars per share)	$ 16.15
Exercise price, high end of range (in dollars per share)	30.36
$36.25 - $54.38
Stock-Based Compensation
Exercise price, low end of range (in dollars per share)	36.25
Exercise price, high end of range (in dollars per share)	54.38
$16.15 - $54.38
Stock-Based Compensation
Exercise price, low end of range (in dollars per share)	16.15
Exercise price, high end of range (in dollars per share)	$ 54.38
Stock Options | $16.15 - $30.36
Options Outstanding
Number of Shares | shares	28
Weighted-Average Remaining Contractual Life	4 years
Weighted-Average Exercise Price (in dollars per share)	$ 28.13
Stock Options | $36.25 - $54.38
Options Outstanding
Number of Shares | shares	42
Weighted-Average Remaining Contractual Life	5 years 8 months 12 days
Weighted-Average Exercise Price (in dollars per share)	$ 39.44
Stock Options | $16.15 - $54.38
Options Outstanding
Number of Shares | shares	70
Weighted-Average Remaining Contractual Life	5 years
Weighted-Average Exercise Price (in dollars per share)	$ 34.97

Stock-Based Compensation - Fair

Stock-Based Compensation - Fair Value Assumptions (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)item$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / shares
Additional information
Stock-based compensation expense	$ 10.6	$ 6.9	$ 5.9
Stock Options
Other information
Total fair value of options vested	$ 0.4
Nonvested Options, Shares
Nonvested at end of year (in shares) | shares	0
Additional information
Vesting period	3 years
Restricted Stock and Restricted Stock Units
Other information
Compensation expense yet to be recognized	$ 1.5
Weighted-average period over which compensation cost will be recognized	1 year 9 months 18 days
Shares
Unvested at beginning of year (in shares) | shares	120,000
Granted (in shares) | shares	67,000
Vested (in shares) | shares	(72,000)
Unvested at end of year (in shares) | shares	115,000	120,000
Weighted Average Grant Date Fair Value
Unvested at beginning of year (in dollars per share) | $ / shares	$ 45.21
Granted (in dollars per share) | $ / shares	76.73	$ 39.03	$ 51.02
Vested (in dollars per share) | $ / shares	54.53
Unvested at end of year (in dollars per share) | $ / shares	$ 57.74	45.21
Additional information
Fair value of shares vested	$ 3.9
Weighted-average fair value (in dollars per share) | $ / shares	$ 76.73	$ 39.03	$ 51.02
Aggregate intrinsic value of restricted stock vested	$ 5.5	$ 2.9	$ 3.5
Performance Stock Units
Other information
Compensation expense yet to be recognized	$ 1.1
Weighted-average period over which compensation cost will be recognized	1 year 4 months 24 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	$ 10.2
Value of PSUs granted	3.6
Stock-based compensation expense	$ 5.7	$ 2.7	$ 1.9
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

Segment Information (Details)

Segment Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)segment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Segment Information
Number of reportable segments | segment	2
Revenue	$ 3,073,636	$ 2,856,659	$ 2,615,277
Gross Profit	563,207	546,983	501,943
Capital Expenditures	22,330	24,131	31,750
Total Assets	2,209,114	1,757,355
Operating | Mechanical Services
Segment Information
Revenue	2,542,623	2,430,632	2,272,031
Gross Profit	486,346	513,760	469,347
Capital Expenditures	19,408	22,561	28,070
Total Assets	1,452,527	1,246,098
Operating | Electrical Services
Segment Information
Revenue	531,013	426,027	343,246
Gross Profit	76,861	33,223	32,596
Capital Expenditures	2,413	944	1,367
Total Assets	690,364	419,475
Corporate & Eliminations
Segment Information
Capital Expenditures	509	626	$ 2,313
Total Assets	$ 66,223	$ 91,782