Goodwill and Other Intangible Assets, Acquired Intangible Assets (Details) - Acquired Finite-Lived Intangible Assets [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 8.0	$ 8.2	$ 7.9
Estimated amortization expense, 2018	7.9
Estimated amortization expense, 2019	7.9
Estimated amortization expense, 2020	7.9
Estimated amortization expense, 2021	7.9
Estimated amortization expense, 2022	7.9
Estimated amortization expense, thereafter	$ 157.0