Leases (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Future minimum lease payments required under leasing arrangements
2012	$ 16,700
2013	14,900
2014	14,200
2015	11,500
2016	8,500
Thereafter	12,000
Total rental expense under operating leases	$ 20,100	$ 21,600	$ 21,100