Leases (Schedule of Cumulative Effects of Adoption of ASC 842) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 187,385	$ 197,755	$ 151,426	$ 183,727
Accounts receivable, net	234,127	223,176
Contract assets	57,869	57,447
Inventories	102,379	85,904
Income taxes prepaid and receivable	6,818	7,473
Prepaid expenses and other current assets	23,696	21,294
Total current assets	612,274	593,049
Property, plant and equipment, net	460,520	462,055
Intangibles, net	47,646	49,206
Goodwill	163,438	164,382
Deferred income taxes	63,736	62,622
Noncurrent receivables	45,354	45,061
Other assets	50,313	41,617
Total assets	1,443,281	1,417,992
LIABILITIES AND SHAREHOLDERS' EQUITY
Accounts payable	74,050	52,246
Accrued liabilities	122,342	129,030
Current maturities of long-term debt	19	1,224
Income taxes payable	8,387	6,806
Total current liabilities	204,798	189,306
Long-term debt	491,022	523,707
Other noncurrent liabilities	112,726	88,277
Deferred taxes and other liabilities	8,328	8,422
Total liabilities	816,874	809,712
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	430,052	430,555
Retained earnings	613,057	589,645
Accumulated items of other comprehensive income:
Translation adjustments	(116,630)	(115,976)
Pension and postretirement liability adjustments	(48,596)	(47,109)
Derivative valuation adjustment	1,846	4,697
Treasury stock (Class A), at cost 0 shares in 2019 and 8,418,620 shares in 2018	(256,603)	(256,603)
Total Company shareholders' equity	623,166	605,249
Noncontrolling interest	3,241	3,031
Total equity	626,407	608,280	$ 592,578	$ 57,301
Total liabilities and shareholders' equity	1,443,281	1,417,992
Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock	37	37
Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock	$ 3	3
Adjustments Increase/(Decrease) [Member]
Assets
Cash and cash equivalents
Accounts receivable, net
Contract assets
Inventories
Income taxes prepaid and receivable
Prepaid expenses and other current assets		(370)
Total current assets		(370)
Property, plant and equipment, net		(6,144)
Intangibles, net
Goodwill
Deferred income taxes		(20)
Noncurrent receivables
Other assets		13,615
Total assets		7,081
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable
Accrued liabilities		4,964
Current maturities of long-term debt		(1,206)
Income taxes payable
Total current liabilities		3,758
Long-term debt		(24,680)
Other noncurrent liabilities		27,968
Deferred taxes and other liabilities
Total liabilities		7,046
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital
Retained earnings		35
Accumulated items of other comprehensive income:
Translation adjustments
Pension and postretirement liability adjustments
Derivative valuation adjustment
Treasury stock (Class A), at cost 0 shares in 2019 and 8,418,620 shares in 2018
Total Company shareholders' equity		35
Noncontrolling interest
Total equity		35
Total liabilities and shareholders' equity		7,081
Opening balance, as adjusted [Member]
Assets
Cash and cash equivalents		197,755
Accounts receivable, net		223,176
Contract assets		57,447
Inventories		85,904
Income taxes prepaid and receivable		7,473
Prepaid expenses and other current assets		20,924
Total current assets		592,679
Property, plant and equipment, net		455,911
Intangibles, net		49,206
Goodwill		164,382
Deferred income taxes		62,602
Noncurrent receivables		45,061
Other assets		55,232
Total assets		1,425,073
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable		52,246
Accrued liabilities		133,994
Current maturities of long-term debt		18
Income taxes payable		6,806
Total current liabilities		193,064
Long-term debt		499,027
Other noncurrent liabilities		116,245
Deferred taxes and other liabilities		8,422
Total liabilities		816,758
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital		430,555
Retained earnings		589,680
Accumulated items of other comprehensive income:
Translation adjustments		(115,976)
Pension and postretirement liability adjustments		(47,109)
Derivative valuation adjustment		4,697
Treasury stock (Class A), at cost 0 shares in 2019 and 8,418,620 shares in 2018		(256,603)
Total Company shareholders' equity		605,284
Noncontrolling interest		3,031
Total equity		608,315
Total liabilities and shareholders' equity		$ 1,425,073