Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accrued Liabilities (Details) [Abstract]
Accrued insurance costs	$ 122,475	$ 124,499
Accrued compensation	55,911	56,748
Deferred revenue	44,506	43,577
Taxes other than income	23,660	27,656
Accrued dividends	12,103	12,188
Deferred rent	10,424	9,699
Accrued interest payable	5,609	3,580
Accrued other	40,547	31,119
Total accrued liabilities	$ 315,235	$ 309,066