v3.8.0.1
Accrued Liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Accrued Liabilities, Current [Abstract]    
Sales volume discounts payable $ 17,386 $ 13,590
Property taxes payable 3,802 3,932
Accrued salaries 8,318 6,198
Other accrued liabilities 5,499 4,266
Total accrued liabilities $ 35,005 $ 27,986