Leases (Schedule of Cumulative Effects of Adoption of ASC 842) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 215,233	$ 187,385	$ 197,755	$ 154,744	$ 151,426	$ 183,727
Accounts receivable, net	220,584		223,176
Contract assets	54,431		57,447
Inventories	104,254		85,904
Income taxes prepaid and receivable	7,165		7,473
Prepaid expenses and other current assets	25,108		21,294
Total current assets	626,775		593,049
Property, plant and equipment, net	458,038		462,055
Intangibles, net	46,089		49,206
Goodwill	164,083		164,382
Deferred income taxes	66,082		62,622
Noncurrent receivables	45,651		45,061
Other assets	51,381		41,617
Total assets	1,458,099		1,417,992
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable	61,899		52,246
Accrued liabilities	120,693		129,030
Current maturities of long-term debt	19		1,224
Income taxes payable	14,078		6,806
Total current liabilities	196,689		189,306
Long-term debt	482,019		523,707
Other noncurrent liabilities	119,642		88,277
Deferred taxes and other liabilities	8,433		8,422
Total liabilities	806,783		809,712
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	431,037		430,555
Retained earnings	641,297		589,645
Accumulated items of other comprehensive income:
Translation adjustments	(116,631)		(115,976)
Pension and postretirement liability adjustments	(48,636)		(47,109)
Derivative valuation adjustment	(2,849)		4,697
Treasury stock (Class A), at cost 8,418,620 shares in 2018 and 8,431,335 shares in 2017	(256,391)		(256,603)
Total Company shareholders' equity	647,868		605,249
Noncontrolling interest	3,448		3,031
Total equity	651,316	626,407	608,280	588,630	592,578	573,015
Total liabilities and shareholders' equity	1,458,099		1,417,992
Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock	39		37
Accumulated items of other comprehensive income:
Total equity	39	37	37	37	37	37
Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock	2		3
Accumulated items of other comprehensive income:
Total equity	$ 2	$ 3		$ 3	$ 3	$ 3
Accounting Standards Update 2018-11 [Member] | 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 8,418,620 shares in 2018 and 8,431,335 shares in 2017
Total Company shareholders' equity			35
Noncontrolling interest
Total equity			35
Total liabilities and shareholders' equity			7,081
Accounting Standards Update 2018-11 [Member] | Adjustments Increase/(Decrease) [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock
Accounting Standards Update 2018-11 [Member] | Adjustments Increase/(Decrease) [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock
Accounting Standards Update 2018-11 [Member] | 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 8,418,620 shares in 2018 and 8,431,335 shares in 2017			(256,603)
Total Company shareholders' equity			605,284
Noncontrolling interest			3,031
Total equity			608,315
Total liabilities and shareholders' equity			1,425,073
Accounting Standards Update 2018-11 [Member] | Opening balance, as adjusted [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock			37
Accounting Standards Update 2018-11 [Member] | Opening balance, as adjusted [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock			$ 3