Accrued Liabilities (Schedule of Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Salaries and wages	$ 22,878	$ 20,821
Contract loss reserve	17,190	20,708
Employee benefits	14,235	12,316
Returns and allowances	11,249	11,343
Accrual for compensated absences	10,445	10,636
Dividends	6,139	5,808
Contract liabilities	5,656	9,025
Lease liability - Operating lease	4,023
Lease liability - Financing lease	1,835
Postretirement medical benefits - current portion	3,808	3,890
Restructuring costs	1,342	5,534
Professional fees	2,999	2,575
Pension liability - current portion	2,155	2,124
Workers' compensation	1,982	1,794
Utilities	790	974
Interest	517	901
Other	18,642	20,581
Total	$ 125,885	$ 129,030