Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accrued Liabilities [Abstract]
Accrued insurance costs	$ 121,844	$ 125,067
Deferred revenue	60,535	58,880
Accrued compensation	42,940	55,354
Taxes other than income	20,081	20,632
Accrued dividends	12,773	12,737
Deferred compensation	10,489	9,653
Deferred rent	6,882	9,585
Accrued interest payable	5,781	5,766
Accrued other	51,228	54,138
Total accrued liabilities	$ 332,553	$ 351,812