Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue
Revenue	$ 833,896	$ 714,099	$ 2,217,552	$ 2,157,698
Percentage of revenue from contract with customer (as a percent)	100.00%	100.00%	100.00%	100.00%
Industrial
Disaggregation of Revenue
Revenue	$ 379,605	$ 268,651	$ 960,263	$ 844,719
Percentage of revenue from contract with customer (as a percent)	45.50%	37.60%	43.30%	39.10%
Education
Disaggregation of Revenue
Revenue	$ 115,536	$ 135,992	$ 300,374	$ 375,580
Percentage of revenue from contract with customer (as a percent)	13.90%	19.00%	13.50%	17.40%
Office Buildings
Disaggregation of Revenue
Revenue	$ 77,806	$ 81,183	$ 229,816	$ 232,349
Percentage of revenue from contract with customer (as a percent)	9.30%	11.40%	10.40%	10.80%
Healthcare
Disaggregation of Revenue
Revenue	$ 101,446	$ 86,061	$ 292,541	$ 281,370
Percentage of revenue from contract with customer (as a percent)	12.20%	12.10%	13.20%	13.00%
Government
Disaggregation of Revenue
Revenue	$ 40,268	$ 40,631	$ 125,939	$ 119,444
Percentage of revenue from contract with customer (as a percent)	4.80%	5.70%	5.70%	5.50%
Retail, Restaurants and Entertainment
Disaggregation of Revenue
Revenue	$ 62,365	$ 64,212	$ 155,874	$ 190,043
Percentage of revenue from contract with customer (as a percent)	7.50%	9.00%	7.00%	8.80%
Multi-Family and Residential
Disaggregation of Revenue
Revenue	$ 29,741	$ 21,776	$ 82,742	$ 61,062
Percentage of revenue from contract with customer (as a percent)	3.60%	3.00%	3.70%	2.80%
Other
Disaggregation of Revenue
Revenue	$ 27,129	$ 15,593	$ 70,003	$ 53,131
Percentage of revenue from contract with customer (as a percent)	3.20%	2.20%	3.20%	2.60%
New Construction
Disaggregation of Revenue
Revenue	$ 397,446	$ 310,000	$ 1,029,397	$ 1,034,833
Percentage of revenue from contract with customer (as a percent)	47.60%	43.40%	46.40%	48.00%
Existing Building Construction
Disaggregation of Revenue
Revenue	$ 250,893	$ 235,798	$ 682,811	$ 668,067
Percentage of revenue from contract with customer (as a percent)	30.10%	33.00%	30.80%	30.90%
Service Projects
Disaggregation of Revenue
Revenue	$ 75,525	$ 69,162	$ 201,848	$ 179,188
Percentage of revenue from contract with customer (as a percent)	9.10%	9.70%	9.10%	8.30%
Service Calls, Maintenance and Monitoring
Disaggregation of Revenue
Revenue	$ 110,032	$ 99,139	$ 303,496	$ 275,610
Percentage of revenue from contract with customer (as a percent)	13.20%	13.90%	13.70%	12.80%
Mechanical Services
Disaggregation of Revenue
Revenue	$ 690,680	$ 625,660	$ 1,868,096	$ 1,823,117
Percentage of revenue from contract with customer (as a percent)	82.80%	87.60%	84.20%	84.50%
Electrical Services
Disaggregation of Revenue
Revenue	$ 143,216	$ 88,439	$ 349,456	$ 334,581
Percentage of revenue from contract with customer (as a percent)	17.20%	12.40%	15.80%	15.50%