Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Other Current Liabilities [Line Items]
Payroll and incentive compensation	$ 16,101	$ 10,499
Union dues and benefits	10,261	8,182
Profit sharing and thrift plan	2,004	1,294
Taxes, other than income taxes	7,639	3,578
Other	6,377	5,303
Other current liabilities, total	$ 42,382	$ 28,856