Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue
Revenue	$ 700,131	$ 538,473
Percentage of revenue from contract with customer (as a percent)	100.00%	100.00%
Industrial
Disaggregation of Revenue
Revenue	$ 275,198	$ 168,660
Percentage of revenue from contract with customer (as a percent)	39.30%	31.30%
Education
Disaggregation of Revenue
Revenue	$ 109,584	$ 66,743
Percentage of revenue from contract with customer (as a percent)	15.70%	12.40%
Office Buildings
Disaggregation of Revenue
Revenue	$ 75,572	$ 66,212
Percentage of revenue from contract with customer (as a percent)	10.80%	12.30%
Healthcare
Disaggregation of Revenue
Revenue	$ 99,259	$ 92,023
Percentage of revenue from contract with customer (as a percent)	14.20%	17.10%
Government
Disaggregation of Revenue
Revenue	$ 38,981	$ 32,279
Percentage of revenue from contract with customer (as a percent)	5.60%	6.00%
Retail, Restaurants and Entertainment
Disaggregation of Revenue
Revenue	$ 61,203	$ 59,391
Percentage of revenue from contract with customer (as a percent)	8.70%	11.00%
Multi-Family and Residential
Disaggregation of Revenue
Revenue	$ 18,731	$ 30,235
Percentage of revenue from contract with customer (as a percent)	2.70%	5.60%
Other
Disaggregation of Revenue
Revenue	$ 21,603	$ 22,930
Percentage of revenue from contract with customer (as a percent)	3.00%	4.30%
New Construction
Disaggregation of Revenue
Revenue	$ 347,400	$ 223,960
Percentage of revenue from contract with customer (as a percent)	49.60%	41.60%
Existing Building Construction
Disaggregation of Revenue
Revenue	$ 207,166	$ 182,296
Percentage of revenue from contract with customer (as a percent)	29.60%	33.80%
Service Projects
Disaggregation of Revenue
Revenue	$ 51,648	$ 50,384
Percentage of revenue from contract with customer (as a percent)	7.40%	9.40%
Service Calls, Maintenance and Monitoring
Disaggregation of Revenue
Revenue	$ 93,917	$ 81,833
Percentage of revenue from contract with customer (as a percent)	13.40%	15.20%
Mechanical Services
Disaggregation of Revenue
Revenue	$ 565,464	$ 534,585
Percentage of revenue from contract with customer (as a percent)	80.80%	99.30%
Electrical Services
Disaggregation of Revenue
Revenue	$ 134,667	$ 3,888
Percentage of revenue from contract with customer (as a percent)	19.20%	0.70%