Accrued Liabilities Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Accrued insurance costs	$ 109,505		$ 124,760
Accrued compensation	55,789		37,783
Deferred revenue	53,348		51,742
Taxes other than income	27,711		27,415
Income taxes payable	26,797		0
Accrued legal settlement	11,000		0
Deferred compensation	8,687		11,323
Accrued interest payable	5,643		5,707
Deferred rent	3,503		3,937
Accrued other	35,476		35,351
Accrued liabilities	$ 337,459	$ 299,683	$ 298,018