Segment Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)
Segment Information
Number of reportable segments | segment	2
Revenue	$ 669,761	$ 700,131
Gross Profit	123,469	117,093
Operating | Mechanical Services Segment
Segment Information
Revenue	565,620	570,751
Gross Profit	108,128	109,984
Operating | Electrical Services
Segment Information
Revenue	104,141	129,380
Gross Profit	$ 15,341	$ 7,109