Foreign Currency Exchange Rate Risk (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Notional amounts of foreign currency forward contracts	$ 129,037	$ 45,145
Remaining maturities of foreign currency forward contracts	6 months or less
Swedish Kronor
Notional amounts of foreign currency forward contracts	98,385	18,091
British Pound Sterling
Notional amounts of foreign currency forward contracts	15,619	3,050
Australian Dollar
Notional amounts of foreign currency forward contracts	7,022	609
Japanese Yen
Notional amounts of foreign currency forward contracts	5,157	3,581
Euro
Notional amounts of foreign currency forward contracts	2,232	19,640
Other
Notional amounts of foreign currency forward contracts	$ 622	$ 174