Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Salaries and wages	$ 17,916	$ 18,520
Accrual for compensated absences	11,223	10,181
Employee benefits	13,553	13,277
Workers' compensation	2,397	2,053
Pension liability - current portion	2,094	2,057
Postretirement medical benefits - current portion	4,108	4,195
Returns and allowances	11,370	13,714
Billings in excess of revenue recognized	2,569	2,334
Contract loss reserve	11,902	56
Professional fees	2,310	3,068
Utilities	910	991
Dividends	5,474	5,458
Restructuring costs	2,714	4,668
Interest	817	1,218
Other	16,557	13,405
Total	$ 105,914	$ 95,195