Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Indefinite-lived Intangible Assets [Line Items]
Intangible assets, amortization expense	$ 19.6	$ 10.9	$ 7.1
Intangible assets, amortization expense 2018	21.7
Intangible assets, amortization expense 2019	21.6
Intangible assets, amortization expense 2020	21.3
Intangible assets, amortization expense 2021	20.9
Intangible assets, amortization expense 2022	$ 20.3