Acquisitions (Details) $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 01, 2016 USD ($)	Mar. 31, 2016 item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Acquisitions
Number of acquisitions | item		2
Goodwill on acquisition			$ 149,208	$ 143,874	$ 140,341
Environmental Air Systems
Acquisitions
Interest acquired (as a percent)	40.00%
Total purchase price	$ 46,600
Purchase price paid in cash	$ 42,000
Shoffner
Acquisitions
Interest acquired (as a percent)		100.00%
Total purchase price			19,800
Purchase price paid in cash			15,500
Revenue in consolidated results			71,900
Amount allocated to goodwill and identifiable intangible assets for acquisitions			14,800
Other Acquisitions
Acquisitions
Total purchase price			$ 100	$ 8,300