Foreign Currency Exchange Rate Risk Foreign Currency Exchange Rate Risk (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Notional amount of foreign currency derivatives	$ 21,630	$ 45,145
Euro
Notional amount of foreign currency derivatives	2,196	19,640
Swedish kronor
Notional amount of foreign currency derivatives	7,042	18,091
British pound sterling
Notional amount of foreign currency derivatives	3,541	3,050
Australian dollar
Notional amount of foreign currency derivatives	1,570	609
Danish kroner
Notional amount of foreign currency derivatives	0	174
Japanese yen
Notional amount of foreign currency derivatives	6,112	3,581
Norwegian krone
Notional amount of foreign currency derivatives	$ 1,169	$ 0