Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities [Abstract]
Payroll and other compensation	$ 53,857	$ 37,560
Deferred revenue and customer advances	40,472	34,812
Pension and other postretirement benefits	8,294	8,261
Accrued income taxes	26,340	26,477
Other	52,278	49,857
Accrued liabilities	$ 181,241	$ 156,967