Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities, Current [Abstract]
High deductible insurance	$ 6,250	$ 6,250
Accrued payroll	19,060	16,060
Other	24,160	24,880
Total accrued liabilities	$ 49,470	$ 47,190