Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accrued Liabilities (Details) [Abstract]
Accrued insurance costs	$ 123,649	$ 138,760
Deferred revenue	46,747	36,620
Accrued compensation	44,967	47,656
Taxes other than income	25,457	24,244
Accrued interest payable	4,422	5,245
Accrued restructuring costs	7,737	1,494
Accrued dividends	9,466
Accrued capital lease obligations	105	816
Accrued other	36,169	33,580
Total accrued liabilities	$ 298,719	$ 288,415