Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue
Revenue	$ 669,761	$ 700,131
Percentage of revenue from contract with customer (as a percent)	100.00%	100.00%
Industrial
Disaggregation of Revenue
Revenue	$ 269,583	$ 275,198
Percentage of revenue from contract with customer (as a percent)	40.30%	39.30%
Education
Disaggregation of Revenue
Revenue	$ 92,457	$ 109,584
Percentage of revenue from contract with customer (as a percent)	13.80%	15.70%
Office Buildings
Disaggregation of Revenue
Revenue	$ 78,996	$ 75,572
Percentage of revenue from contract with customer (as a percent)	11.80%	10.80%
Healthcare
Disaggregation of Revenue
Revenue	$ 95,091	$ 99,259
Percentage of revenue from contract with customer (as a percent)	14.20%	14.20%
Government
Disaggregation of Revenue
Revenue	$ 43,165	$ 38,981
Percentage of revenue from contract with customer (as a percent)	6.40%	5.60%
Retail, Restaurants and Entertainment
Disaggregation of Revenue
Revenue	$ 44,576	$ 61,203
Percentage of revenue from contract with customer (as a percent)	6.70%	8.70%
Multi-Family and Residential
Disaggregation of Revenue
Revenue	$ 24,660	$ 18,731
Percentage of revenue from contract with customer (as a percent)	3.70%	2.70%
Other
Disaggregation of Revenue
Revenue	$ 21,233	$ 21,603
Percentage of revenue from contract with customer (as a percent)	3.10%	3.00%
New Construction
Disaggregation of Revenue
Revenue	$ 302,061	$ 347,400
Percentage of revenue from contract with customer (as a percent)	45.10%	49.60%
Existing Building Construction
Disaggregation of Revenue
Revenue	$ 216,601	$ 207,166
Percentage of revenue from contract with customer (as a percent)	32.30%	29.60%
Service Projects
Disaggregation of Revenue
Revenue	$ 60,060	$ 51,648
Percentage of revenue from contract with customer (as a percent)	9.00%	7.40%
Service Calls, Maintenance and Monitoring
Disaggregation of Revenue
Revenue	$ 91,039	$ 93,917
Percentage of revenue from contract with customer (as a percent)	13.60%	13.40%
Mechanical Services
Disaggregation of Revenue
Revenue	$ 565,620	$ 570,751
Percentage of revenue from contract with customer (as a percent)	84.50%	81.50%
Electrical Services
Disaggregation of Revenue
Revenue	$ 104,141	$ 129,380
Percentage of revenue from contract with customer (as a percent)	15.50%	18.50%