Intangible Assets - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 30.8	$ 29.5
Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	10 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	20 years
Weighted average
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	15 years