Leases (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Future minimum lease payments required under leasing arrangements
2013	$ 18,600
2014	16,300
2015	13,800
2016	10,700
2017	10,200
Thereafter	12,500
Total rental expense under operating leases	$ 22,000	$ 20,100	$ 21,600