Business Combinations, Goodwill and Intangible Assets, Identifiable Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Identifiable intangible assets
Original cost		$ 43.9	$ 34.7
Accumulated amortization		(11.5)	(9.7)
Net book value		32.4	25.0
Impairment of Intangible Assets	$ 2.6
Amortization of definite-lived intangible assets		$ 1.8	$ 1.4	$ 1.5
Noncompete Agreements
Finite-Lived Intangible Assets
Weighted-Average Amortization Period (in years)		5 years
Identifiable intangible assets
Original cost		$ 5.4
Accumulated amortization		(0.3)
Net book value		$ 5.1
Trade Names
Finite-Lived Intangible Assets
Weighted-Average Amortization Period (in years)		10 years
Identifiable intangible assets
Original cost		$ 2.4
Accumulated amortization		(0.1)
Net book value		$ 2.3
Customer relationships
Finite-Lived Intangible Assets
Weighted-Average Amortization Period (in years)		24 years	25 years
Identifiable intangible assets
Original cost		$ 36.1	$ 34.7
Accumulated amortization		(11.1)	(9.7)
Net book value		$ 25.0	$ 25.0