CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 154,744	$ 151,426	$ 183,727	$ 138,792	$ 143,333	$ 181,742
Accounts receivable, net	249,482		202,675
Contract assets	59,244
Inventories	97,659		136,519
Income taxes prepaid and receivable	6,087		6,266
Prepaid expenses and other current assets	19,559		14,520
Total current assets	586,775		543,707
Property, plant and equipment, net	450,694		454,302
Intangibles, net	52,322		55,441
Goodwill	165,474		166,796
Deferred income taxes	81,237		68,648
Noncurrent receivables	36,981		32,811
Other assets	48,978		39,493
Total assets	1,422,461		1,361,198
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable	26		262
Accounts payable	54,752		44,899
Accrued liabilities	125,255		105,914
Current maturities of long-term debt	1,844		1,799
Income taxes payable	14,620		8,643
Total current liabilities	196,497		161,517
Long-term debt	523,186		514,120
Other noncurrent liabilities	97,563		101,555
Deferred taxes and other liabilities	13,556		10,991
Total liabilities	830,802		788,183
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	429,635		428,423
Retained earnings	558,639		534,082
Accumulated items of other comprehensive income:
Translation adjustments	(102,888)		(87,318)
Pension and postretirement liability adjustments	(48,422)		(50,536)
Derivative valuation adjustment	8,155		1,953
Treasury stock (Class A), at cost 8,418,620 shares in 2018 and 8,431,335 shares in 2017	(256,602)		(256,876)
Total Company shareholders' equity	588,557		569,768
Noncontrolling interest	3,102		3,247
Total equity	591,659		573,015
Total liabilities and shareholders' equity	1,422,461		1,361,198
Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock	37		37
Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock	$ 3		$ 3