Selected Unaudited Quarterly Information - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Revenues (in US dollars)	$ 2,229,308	$ 2,047,049	$ 1,953,886	$ 1,900,388	$ 2,012,639	$ 1,886,691	$ 1,895,937	$ 1,891,732	$ 8,130,631	$ 7,686,999	$ 7,551,524
Gross profit (in US dollars)	336,151	309,339	290,844	269,119	311,101	295,070	274,501	266,340	1,205,453	1,147,012	1,037,862
Impairment loss on goodwill and identifiable intangible assets	0	0	907	0	57,819	0	0	0	907	57,819	2,428
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
Basic earnings (loss) per common share:
Basic EPS from continuing operations (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
Basic EPS 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:
Diluted EPS from continuing operations (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
Diluted EPS 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