Foreign Currency Exchange Rate Risk (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Notional amounts of foreign currency forward contracts	$ 45,145	$ 66,802
Remaining maturities of foreign currency forward contracts	45 days or less
Euro
Notional amounts of foreign currency forward contracts	19,640	41,022
Swedish Kronor
Notional amounts of foreign currency forward contracts	18,091	23,212
British Pound Sterling
Notional amounts of foreign currency forward contracts	3,050	1,551
Australian Dollar
Notional amounts of foreign currency forward contracts	609	1,017
Danish Kroner
Notional amounts of foreign currency forward contracts	174	0
Japanese Yen
Notional amounts of foreign currency forward contracts	$ 3,581	$ 0