Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue
Revenue	$ 713,895	$ 743,468	$ 1,383,656	$ 1,443,599
Percentage of revenue from contract with customer (as a percent)	100.00%	100.00%	100.00%	100.00%
Industrial
Disaggregation of Revenue
Revenue	$ 311,075	$ 300,870	$ 580,658	$ 576,068
Percentage of revenue from contract with customer (as a percent)	43.60%	40.50%	42.00%	39.90%
Education
Disaggregation of Revenue
Revenue	$ 92,381	$ 130,004	$ 184,838	$ 239,588
Percentage of revenue from contract with customer (as a percent)	12.90%	17.50%	13.40%	16.60%
Office Buildings
Disaggregation of Revenue
Revenue	$ 73,014	$ 75,594	$ 152,010	$ 151,166
Percentage of revenue from contract with customer (as a percent)	10.20%	10.20%	11.00%	10.50%
Healthcare
Disaggregation of Revenue
Revenue	$ 96,004	$ 96,050	$ 191,095	$ 195,309
Percentage of revenue from contract with customer (as a percent)	13.40%	12.90%	13.80%	13.50%
Government
Disaggregation of Revenue
Revenue	$ 42,506	$ 39,832	$ 85,671	$ 78,813
Percentage of revenue from contract with customer (as a percent)	6.00%	5.40%	6.20%	5.50%
Retail, Restaurants and Entertainment
Disaggregation of Revenue
Revenue	$ 48,933	$ 64,628	$ 93,509	$ 125,831
Percentage of revenue from contract with customer (as a percent)	6.90%	8.70%	6.70%	8.70%
Multi-Family and Residential
Disaggregation of Revenue
Revenue	$ 28,341	$ 20,555	$ 53,001	$ 39,286
Percentage of revenue from contract with customer (as a percent)	4.00%	2.80%	3.80%	2.70%
Other
Disaggregation of Revenue
Revenue	$ 21,641	$ 15,935	$ 42,874	$ 37,538
Percentage of revenue from contract with customer (as a percent)	3.00%	2.00%	3.10%	2.60%
New Construction
Disaggregation of Revenue
Revenue	$ 329,890	$ 377,433	$ 631,951	$ 724,833
Percentage of revenue from contract with customer (as a percent)	46.20%	50.80%	45.70%	50.20%
Existing Building Construction
Disaggregation of Revenue
Revenue	$ 215,317	$ 225,103	$ 431,918	$ 432,269
Percentage of revenue from contract with customer (as a percent)	30.20%	30.30%	31.20%	29.90%
Service Projects
Disaggregation of Revenue
Revenue	$ 66,263	$ 58,378	$ 126,323	$ 110,026
Percentage of revenue from contract with customer (as a percent)	9.30%	7.80%	9.10%	7.60%
Service Calls, Maintenance and Monitoring
Disaggregation of Revenue
Revenue	$ 102,425	$ 82,554	$ 193,464	$ 176,471
Percentage of revenue from contract with customer (as a percent)	14.30%	11.10%	14.00%	12.30%
Mechanical Services
Disaggregation of Revenue
Revenue	$ 611,796	$ 626,706	$ 1,177,416	$ 1,197,457
Percentage of revenue from contract with customer (as a percent)	85.70%	84.30%	85.10%	82.90%
Electrical Services
Disaggregation of Revenue
Revenue	$ 102,099	$ 116,762	$ 206,240	$ 246,142
Percentage of revenue from contract with customer (as a percent)	14.30%	15.70%	14.90%	17.10%