New Accounting Pronouncements - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in retained deficit	$ (742,300,000)	$ (831,600,000)
Classification of excess income tax benefits on share-based compensation awards within operating activities	47,600,000	$ 6,500,000	$ (38,500,000)
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Classification of excess income tax benefits on share-based compensation awards within operating activities	600,000
Benefit for excess tax benefits related to stock compensation awards	$ (0.6)
Scenario, Forecast [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in retained deficit				$ 6,000,000