Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator
Income from continuing operations attributable to EMCOR Group, Inc. common stockholders (in US dollars)									$ 285,876	$ 228,053	$ 185,077
Loss from discontinued operation, net of income taxes (in US dollars)									(2,345)	(857)	(3,142)
Net income attributable to EMCOR Group, Inc. (in US dollars)	$ 77,968	$ 79,373	$ 70,816	$ 55,374	$ 53,201	$ 64,597	$ 56,758	$ 52,640	$ 283,531	$ 227,196	$ 181,935
Denominator
Weighted average shares outstanding used to compute basic earnings (loss) per common share (in shares)									58,112,838	59,254,256	60,769,808
Effect of dilutive securities-Share-based awards (in shares)									330,629	364,713	436,984
Shares used to compute diluted earnings (loss) per common share (in shares)									58,443,467	59,618,969	61,206,792
Basic earnings (loss) per common share:
From continuing operations attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	$ 1.39	$ 1.37	$ 1.22	$ 0.95	$ 0.91	$ 1.10	$ 0.96	$ 0.89	$ 4.92	$ 3.85	$ 3.05
From discontinued operation (in US dollars per share)	(0.02)	(0.01)	0.00	0.00	0.00	0.00	0.00	(0.01)	(0.04)	(0.01)	(0.05)
Net income attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	1.37	1.36	1.22	0.95	0.91	1.10	0.96	0.88	4.88	3.84	3.00
Diluted earnings (loss) per common share:
From continuing operations attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	1.38	1.36	1.21	0.94	0.90	1.09	0.95	0.88	4.89	3.83	3.02
From discontinued operation (in US dollars per share)	(0.02)	(0.01)	0.00	0.00	0.00	0.00	0.00	(0.01)	(0.04)	(0.01)	(0.05)
Net income attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	$ 1.36	$ 1.35	$ 1.21	$ 0.94	$ 0.90	$ 1.09	$ 0.95	$ 0.87	$ 4.85	$ 3.82	$ 2.97