Derivative Instruments (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011 agreement
Senior notes, 4.5 percent due 2021
Derivative Instruments
Debt instrument, face amount	$ 400,000,000
Forward exchange contracts
Derivative Instruments
Derivative maturity period, less than (in months)	6 months
Derivatives not designated as hedging instruments
Derivative Instruments
Asset Derivatives	17,000	3,325,000
Liability Derivatives	3,646,000	60,000
Derivatives not designated as hedging instruments | Forward exchange contracts
Derivative Instruments
Notional amounts of derivatives	9,700,000	9,800,000
Asset Derivatives	17,000	57,000
Liability Derivatives	14,000	60,000
Derivatives designated as hedging instruments | Interest-rate swap
Derivative Instruments
Notional amounts of derivatives		400,000,000
Number of swap agreements		4
Fixed-rate (as a percent)	4.50%
Reference rate for variable rate	six-month London Interbank Offered Rate (LIBOR)
Net settlement benefit due to reset of variable rates semi-annually at each net settlement date	1,800,000
Asset Derivatives		3,268,000
Liability Derivatives	$ 3,632,000