Derivatives and Hedging Activities - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) derivative	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) derivative	Jun. 30, 2017 USD ($)	Dec. 31, 2017 derivative	Jun. 30, 2015 EUR (€)	Mar. 31, 2015 USD ($)
Derivative [Line Items]
Unrealized gain on derivative instruments, net of taxes			$ 13.7	$ (50.6)
4.50% Senior Notes due September 2023
Derivative [Line Items]
Debt interest rate	4.50%		4.50%
Foreign currency forward contracts | Net Investment Hedge
Derivative [Line Items]
Notional amount of outstanding derivative | €						€ 270,000,000
Cumulative translation adjustment loss before tax	$ 3.5		$ 3.5
Cumulative translation adjustment loss, after tax	2.2		$ 2.2
Foreign currency forward contracts | Designated as Hedging Instruments
Derivative [Line Items]
Maximum original maturity of foreign currency forward contracts			12 months
Unrealized gain on derivative instruments, net of taxes	$ 1.3	$ (1.9)	$ 2.4	$ (4.8)
Net unrealized derivative gains included in AOCI to be reclassified into earnings in next twelve months			$ 1.1
Foreign currency forward contracts | Derivatives not designated as hedging instruments
Derivative [Line Items]
Maximum original maturity of foreign currency forward contracts			12 months
Interest rate swaps
Derivative [Line Items]
Number of derivative instruments outstanding | derivative	0		0		0
EUR - Denominated debt | Net Investment Hedge | 4.50% Senior Notes due September 2023
Derivative [Line Items]
Debt instrument face amount | €						€ 400,000,000
Debt interest rate						4.50%
EUR - Denominated debt | Designated as Hedging Instruments | Net Investment Hedge
Derivative [Line Items]
Fair value of liability derivatives	$ 12.8		$ 12.8
Fair value of liability derivatives, after tax	5.9		5.9
Cross-currency swaps | Net Investment Hedge
Derivative [Line Items]
Notional amount of outstanding derivative							$ 425.0
Cross-currency swaps | Designated as Hedging Instruments | Net Investment Hedge
Derivative [Line Items]
Fair value of liability derivatives	$ 61.9		61.9
Semi-annual interest settlement resulted in AOCI			17.7
Semi-annual interest settlement resulted in AOCI after tax			$ (44.2)