Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivative Instruments
Maximum Remaining Maturity of Foreign Currency Derivatives	6 months
Notes Payable 4.5 Percent Due 2021 [Member]
Derivative Instruments
Debt instrument, face amount	$ 400.0
Fixed-rate (as a percent)	4.50%
Derivatives not designated as hedging instruments | Forward exchange contracts
Derivative Instruments
Notional amounts of derivatives	$ 2.8	$ 2.3
Designated as Hedging Instrument [Member] | Interest-rate swap
Derivative Instruments
Notional amounts of derivatives	$ 400.0
Number of swap agreements	4
(Level 2) | Measured on a recurring basis
Derivative Instruments
Derivative Asset	$ 12.4	1.0
(Level 2) | Measured on a recurring basis | Forward exchange contracts
Derivative Instruments
Derivative Asset	0.5	0.0
(Level 2) | Measured on a recurring basis | Interest-rate swap
Derivative Instruments
Derivative Asset	$ 11.9	$ 1.0