Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets, Current [Abstract]
Cash and cash equivalents	$ 253,330	$ 241,316
Accounts receivable, net	190,937	188,423
Contract assets, net	113,225	139,289
Inventories	120,665	110,478
Income taxes prepaid and receivable	6,236	5,940
Prepaid expenses and other current assets	33,089	31,830
Total current assets	717,482	717,276
Property, plant and equipment, net	438,392	448,554
Intangibles, net	42,998	46,869
Goodwill	185,293	187,553
Deferred income taxes	33,102	38,757
Noncurrent receivables, net	34,466	36,265
Other assets	74,907	74,662
Total assets	1,526,640	1,549,936
Liabilities, Current [Abstract]
Accounts payable	55,348	49,173
Accrued liabilities	108,007	125,459
Current maturities of long-term debt	0	9
Income taxes payable	12,233	16,222
Total current liabilities	175,588	190,863
Long-term debt	350,000	398,000
Other noncurrent liabilities	121,333	130,424
Deferred taxes and other liabilities	11,660	10,784
Total liabilities	658,581	730,071
SHAREHOLDERS' EQUITY
Preferred stock	0	0
Additional paid in capital	435,230	433,696
Retained earnings	816,778	770,746
Accumulated items of other comprehensive income:
Translation adjustments	(85,384)	(83,203)
Pension and postretirement liability adjustments	(39,282)	(39,661)
Derivative valuation adjustment	(7,398)	(9,544)
Treasury stock	(255,768)	(256,009)
Total Company shareholders' equity	864,217	816,066
Noncontrolling interest	3,842	3,799
Total equity	868,059	819,865
Total liabilities and shareholders' equity	1,526,640	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