Acquisitions (Details)		3 Months Ended					12 Months Ended
	Jan. 01, 2016 USD ($)	Sep. 30, 2018 item	Jun. 30, 2018 item	Mar. 31, 2018 item	Jun. 30, 2017 USD ($)	Mar. 31, 2016 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) item
Acquisitions
Total purchase price							$ 95,600,000	$ 9,400,000
Number of acquisitions | item		2	3	2		2		4
Number of acquisitions reported as separate operating location | item		1
Environmental Air Systems
Acquisitions
Total purchase price	$ 46,600,000
Purchase price paid in cash	$ 42,000,000
Interest acquired (as a percent)	40.00%
Shoffner
Acquisitions
Total purchase price						$ 19,800,000
Amount allocated to goodwill and identifiable intangible assets for acquisitions						14,800,000
Purchase price paid in cash						$ 15,500,000
Interest acquired (as a percent)						100.00%
BCH
Acquisitions
Total purchase price					$ 121,300,000
Amount allocated to goodwill and identifiable intangible assets for acquisitions					97,000,000
Purchase price paid in cash					95,400,000
Promissory note payable					14,300,000
Contingent earn-out obligation					$ 11,600,000
Other Acquisitions
Acquisitions
Total purchase price						$ 100,000.00000
Number of acquisitions | item						1