Business Combinations, Goodwill and Intangible Assets, Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, gross		$ 37.2
Impairment of the carrying value of goodwill		(18.4)
Goodwill		18.8
Goodwill, acquired		25.2
Goodwill impairment	$ 18.4	0.0	$ 18.4	$ 0.0
Goodwill, total increase		25.2
Goodwill, gross		62.4	37.2
Impairment of the carrying value of goodwill		(18.4)	(18.4)
Goodwill		$ 44.0	$ 18.8
Period over which goodwill is expected to be deductible for income tax purposes		15 years