Derivative Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 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	$ 3.8	$ 2.3
Derivatives designated as hedging instruments | Interest-rate swap
Derivative Instruments
Notional amounts of derivatives	$ 400.0
Number of swap agreements	4
(Level 2) | Measured on a recurring basis | Interest-rate swap
Derivative Instruments
Derivative Asset	$ 5.2	$ 1.0