Business and Organization (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business and Organization
Revenue	$ 461,072	$ 480,851	$ 465,411	$ 380,588	$ 392,100	$ 428,760	$ 427,538	$ 385,942	$ 1,787,922	$ 1,634,340	$ 1,580,519
Percentage of revenue attributable to services									100.00%
Installation of systems in newly constructed facilities
Business and Organization
Percentage of revenue attributable to services									38.00%
Maintenance, repair and replacement services
Business and Organization
Percentage of revenue attributable to services									62.00%
HVAC
Business and Organization
Revenue									$ 1,615,468
Percentage of revenue attributable to services									90.00%
Building Automation Control Systems
Business and Organization
Revenue									$ 94,041
Percentage of revenue attributable to services									5.00%
Other
Business and Organization
Revenue									$ 78,413
Percentage of revenue attributable to services									5.00%