Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities, Current [Abstract]
High deductible insurance	$ 6,090	$ 6,250
Accrued payroll	20,830	19,060
Other	21,380	24,160
Total accrued liabilities	$ 48,300	$ 49,470