Earnings Per Share (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
Numerator
Income from continuing operations attributable to EMCOR Group, Inc. common stockholders (in US dollars)									$ 228,053	$ 185,077	$ 172,346
Loss from discontinued operation, net of income taxes (in US dollars)									(857)	(3,142)	(60)
Net income attributable to EMCOR Group, Inc. (in US dollars)	$ 53,201	$ 64,597	$ 56,758	$ 52,640	$ 40,676	$ 51,531	$ 55,380	$ 34,348	$ 227,196	$ 181,935	$ 172,286
Denominator
Weighted average shares outstanding used to compute basic earnings (loss) per common share (in shares)									59,254,256	60,769,808	62,789,120
Effect of dilutive securities-Share-based awards (in shares)									364,713	436,984	518,392
Shares used to compute diluted earnings (loss) per common share (in shares)									59,618,969	61,206,792	63,307,512
Basic earnings (loss) per common share:
From continuing operations attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	$ 0.91	$ 1.10	$ 0.96	$ 0.89	$ 0.70	$ 0.85	$ 0.93	$ 0.57	$ 3.85	$ 3.05	$ 2.74
From discontinued operation (in US dollars per share)	0.00	0.00	0.00	(0.01)	(0.03)	(0.01)	(0.02)	0.00	(0.01)	(0.05)	0.00
Net income attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	0.91	1.10	0.96	0.88	0.67	0.84	0.91	0.57	3.84	3.00	2.74
Diluted earnings (loss) per common share:
From continuing operations attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	0.90	1.09	0.95	0.88	0.69	0.85	0.92	0.56	3.83	3.02	2.72
From discontinued operation (in US dollars per share)	0.00	0.00	0.00	(0.01)	(0.03)	(0.01)	(0.02)	0.00	(0.01)	(0.05)	0.00
Net income attributable to EMCOR Group, Inc. common stockholders (in US dollars per share)	$ 0.90	$ 1.09	$ 0.95	$ 0.87	$ 0.66	$ 0.84	$ 0.90	$ 0.56	$ 3.82	$ 2.97	$ 2.72