Income Taxes - Operating Loss Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Document Fiscal Year Focus	2017
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Loss carryforwards	$ 963.6
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards subject to expiration	129.2
Operating loss carryforwards not subject to expiration	834.4
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Loss carryforwards	$ 82.4	$ 84.2
Minimum [Member] | Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Expiration date	Dec. 31, 2018
Minimum [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Expiration date	Dec. 31, 2018
Maximum [Member] | Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Expiration date	Dec. 31, 2037
Maximum [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Expiration date	Dec. 31, 2037