Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator
Net income (loss) attributable to EMCOR Group, Inc. common stockholders (in US dollars)	$ 97,350	$ (83,689)	$ 182,124	$ (8,024)
Denominator
Weighted average shares outstanding used to compute basic earnings (loss) per common share (in shares)	54,301,466	54,937,038	54,594,208	55,467,799
Effect of dilutive securities-Share-based awards (in shares)	286,347	0	262,551	0
Shares used to compute diluted earnings (loss) per common share (in shares)	54,587,813	54,937,038	54,856,759	55,467,799
Basic earnings (loss) per common share (in US dollars per share)	$ 1.79	$ (1.52)	$ 3.34	$ (0.14)
Diluted earnings (loss) per common share (in US dollars per share)	$ 1.78	$ (1.52)	$ 3.32	$ (0.14)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive share-based awards excluded from calculation of diluted earnings per share (in shares)	1,500	197,470	14,136	200,538
Assuming dilution, anti-dilutive share-based awards excluded from calculation of diluted earnings per share (in shares)		94,355		94,355