Lease Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Lease Obligations
Net rental expense	$ 181,000,000	$ 166,000,000	$ 228,000,000
Obligations for minimum rentals under non-cancelable operating leases
2013	49,100,000
2014	51,600,000
2015	40,300,000
2016	34,000,000
2017	30,400,000
Thereafter	$ 86,800,000