Foreign Currency Exchange Rate Risk Foreign Currency Exchange Rate Risk (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Notional amount of foreign currency derivatives	$ 21,374	$ 45,145
Euro
Notional amount of foreign currency derivatives	3,645	19,640
Swedish kronor
Notional amount of foreign currency derivatives	3,647	18,091
British pound sterling
Notional amount of foreign currency derivatives	6,686	3,050
Australian dollar
Notional amount of foreign currency derivatives	2,361	609
Danish kroner
Notional amount of foreign currency derivatives	520	174
Japanese yen
Notional amount of foreign currency derivatives	$ 4,515	$ 3,581