Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accrued Liabilities [Abstract]
Accrued insurance costs	$ 125,172	$ 121,844
Deferred revenue	58,255	60,535
Accrued compensation	40,551	42,940
Taxes other than income	22,556	20,081
Deferred compensation	11,394	10,489
Accrued dividends	4,262	12,773
Accrued interest payable	5,808	5,781
Deferred rent	5,199	6,882
Accrued other	58,999	51,228
Total accrued liabilities	$ 332,196	$ 332,553