Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Data (Unaudited)
Revenue	$ 461,072	$ 480,851	$ 465,411	$ 380,588	$ 392,100	$ 428,760	$ 427,538	$ 385,942	$ 1,787,922	$ 1,634,340	$ 1,580,519
Gross Profit	93,731	100,858	95,738	75,954	88,265	92,816	89,426	73,502	366,281	344,009	318,129
Net income including noncontrolling interests	7,539	22,284	17,972	7,477	16,867	20,471	17,717	9,841	55,272	64,896	57,440
Net income attributable to Comfort Systems USA, Inc.	$ 7,539	$ 22,284	$ 17,972	$ 7,477	$ 16,867	$ 20,471	$ 17,717	$ 9,841	$ 55,272	$ 64,896	$ 49,364
Basic-
Basic (in dollars per share)	$ 0.20	$ 0.60	$ 0.48	$ 0.20	$ 0.45	$ 0.55	$ 0.47	$ 0.26	$ 1.48	$ 1.74	$ 1.32
Diluted-
Diluted (in dollars per share)	$ 0.20	$ 0.59	$ 0.48	$ 0.20	$ 0.45	$ 0.54	$ 0.47	$ 0.26	$ 1.47	$ 1.72	$ 1.30
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)	$ 9,500								$ 9,500