Acquisitions - Other Acquisitions (Details) - USD ($) $ in Millions				3 Months Ended
	Dec. 31, 2021	Dec. 01, 2021	Apr. 01, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
MEP Holdings
Acquisitions
Total purchase price	$ 57.3
Purchase price paid in cash	45.2
Promissory note payable	7.6
Mechanical Contractor Kentucky
Acquisitions
Total purchase price	21.1
Mechanical Contractor Indiana
Acquisitions
Total purchase price	$ 4.6
Ivey
Acquisitions
Total purchase price		$ 78.8
Purchase price paid in cash		64.1
Promissory note payable		8.0
Other amount payable		$ 0.4
TAS Energy
Acquisitions
Total purchase price			$ 169.5
Purchase price allocated to goodwill and identifiable intangible assets			126.2
Purchase price paid in cash			105.9
Working capital adjustment			40.5
Promissory note payable			14.0
Contingent earn-out obligation			$ 9.1
TEC
Acquisitions
Total purchase price					$ 88.9
Purchase price paid in cash					73.0
Working capital adjustment					1.3
Promissory note payable					7.0
Contingent earn-out obligation					$ 7.6
Electrical Contractor North Carolina
Acquisitions
Total purchase price						$ 41.6
Mechanical Contractor Utah
Acquisitions
Total purchase price				$ 18.1