Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Payroll and other compensation	$ 46,850		$ 53,857
Contract liabilities	57,522		44,600
Pension and other postretirement benefits	8,618		8,294
Accrued income taxes	30,391		26,340
Other	63,401		48,150
Accrued liabilities	$ 206,782	$ 194,777	$ 181,241