Foreign Currency Exchange Rate Risk Foreign Currency Exchange Rate Risk (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Notional amount of foreign currency derivatives	$ 126,893	$ 129,037
Swedish kronor
Notional amount of foreign currency derivatives	103,462	98,385
British pound sterling
Notional amount of foreign currency derivatives	5,478	15,619
Australian dollar
Notional amount of foreign currency derivatives	6,094	7,022
Japanese yen
Notional amount of foreign currency derivatives	6,296	5,157
Euro
Notional amount of foreign currency derivatives	5,393	2,232
Other
Notional amount of foreign currency derivatives	$ 170	$ 622