Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets, Current [Abstract]
Cash and cash equivalents	$ 237,871	$ 241,316
Accounts receivable, net	188,066	188,423
Contract assets, net	121,767	139,289
Inventories	117,022	110,478
Income taxes prepaid and receivable	7,362	5,940
Prepaid expenses and other current assets	32,306	31,830
Total current assets	704,394	717,276
Property, plant and equipment, net	435,976	448,554
Intangibles, net	44,675	46,869
Goodwill	184,374	187,553
Deferred income taxes	33,436	38,757
Noncurrent receivables, net	34,945	36,265
Other assets	74,366	74,662
Total assets	1,512,166	1,549,936
Liabilities, Current [Abstract]
Accounts payable	54,533	49,173
Accrued liabilities	104,988	125,459
Current maturities of long-term debt	2	9
Income taxes payable	7,439	16,222
Total current liabilities	166,962	190,863
Long-term debt	384,000	398,000
Other noncurrent liabilities	124,167	130,424
Deferred taxes and other liabilities	10,826	10,784
Total liabilities	685,955	730,071
SHAREHOLDERS' EQUITY
Preferred stock	0	0
Additional paid in capital	433,811	433,696
Retained earnings	791,854	770,746
Accumulated items of other comprehensive income:
Translation adjustments	(99,158)	(83,203)
Pension and postretirement liability adjustments	(39,152)	(39,661)
Derivative valuation adjustment	(8,792)	(9,544)
Treasury stock	(256,009)	(256,009)
Total Company shareholders' equity	822,595	816,066
Noncontrolling interest	3,616	3,799
Total equity	826,211	819,865
Total liabilities and shareholders' equity	1,512,166	1,549,936
Common Class A
SHAREHOLDERS' EQUITY
Common stock, par value	39	39
Common Class B
SHAREHOLDERS' EQUITY
Common stock, par value	$ 2	$ 2