Revenue Recognition (Schedule of Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 160,593	$ 154,744	$ 183,727	$ 153,465	$ 138,792	$ 181,742
Accounts receivable, net	252,464		202,675
Contract assets	56,100
Inventories	99,765		136,519
Income taxes prepaid and receivable	6,643		6,266
Prepaid expenses and other current assets	20,541		14,520
Total current assets	596,106		543,707
Property, plant and equipment, net	462,438		454,302
Intangibles, net	50,765		55,441
Goodwill	165,103		166,796
Deferred income taxes	79,865		68,648
Noncurrent receivables	41,657		32,811
Other assets	52,392		39,493
Total assets	1,448,326		1,361,198
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable			262
Accounts payable	51,373		44,899
Accrued liabilities	132,219		105,914
Current maturities of long-term debt	1,231		1,799
Income taxes payable	20,725		8,643
Total current liabilities	205,548		161,517
Long-term debt	529,003		514,120
Other noncurrent liabilities	92,218		101,555
Deferred taxes and other liabilities	12,915		10,991
Total liabilities	839,684		788,183
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	430,231		428,423
Retained earnings	581,369		534,082
Accumulated items of other comprehensive income:
Translation adjustments	(110,900)		(87,318)
Pension and postretirement liability adjustments	(48,293)		(50,536)
Derivative valuation adjustment	9,432		1,953
Treasury stock (Class A), at cost 8,418,620 shares in 2018 and 8,431,335 shares in 2017	(256,603)		(256,876)
Total Company shareholders' equity	605,276		569,768
Noncontrolling interest	3,366		3,247
Total equity	608,642		573,015
Total liabilities and shareholders' equity	1,448,326		1,361,198
Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock	37		37
Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock	3		$ 3
As reported [Member]
ASSETS
Cash and cash equivalents	160,593
Accounts receivable, net	252,464
Contract assets	56,100
Inventories	99,765
Income taxes prepaid and receivable	6,643
Prepaid expenses and other current assets	20,541
Total current assets	596,106
Property, plant and equipment, net	462,438
Intangibles, net	50,765
Goodwill	165,103
Deferred income taxes	79,865
Noncurrent receivables	41,657
Other assets	52,392
Total assets	1,448,326
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable	51,373
Accrued liabilities	132,219
Current maturities of long-term debt	1,231
Income taxes payable	20,725
Total current liabilities	205,548
Long-term debt	529,003
Other noncurrent liabilities	92,218
Deferred taxes and other liabilities	12,915
Total liabilities	839,684
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	430,231
Retained earnings	581,369
Accumulated items of other comprehensive income:
Translation adjustments	(110,900)
Pension and postretirement liability adjustments	(48,293)
Derivative valuation adjustment	9,432
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	605,276
Noncontrolling interest	3,366
Total equity	608,642
Total liabilities and shareholders' equity	1,448,326
As reported [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock	37
As reported [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock	3
Adjustments to reverse effects of ASC 606 [Member]
ASSETS
Cash and cash equivalents
Accounts receivable, net	(8,784)
Contract assets	(56,100)
Inventories	50,458
Income taxes prepaid and receivable
Prepaid expenses and other current assets
Total current assets	(14,426)
Property, plant and equipment, net
Intangibles, net
Goodwill
Deferred income taxes	(217)
Noncurrent receivables
Other assets	(1,256)
Total assets	(15,899)
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable
Accrued liabilities	(19,076)
Current maturities of long-term debt
Income taxes payable
Total current liabilities	(19,076)
Long-term debt
Other noncurrent liabilities
Deferred taxes and other liabilities	(52)
Total liabilities	(19,128)
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital
Retained earnings	2,325
Accumulated items of other comprehensive income:
Translation adjustments	688
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	3,013
Noncontrolling interest	216
Total equity	3,229
Total liabilities and shareholders' equity	(15,899)
Adjustments to reverse effects of ASC 606 [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock
Adjustments to reverse effects of ASC 606 [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock
As adjusted to exclude adoption of ASC 606 [Member]
ASSETS
Cash and cash equivalents	160,593
Accounts receivable, net	243,680
Contract assets
Inventories	150,223
Income taxes prepaid and receivable	6,643
Prepaid expenses and other current assets	20,541
Total current assets	581,680
Property, plant and equipment, net	462,438
Intangibles, net	50,765
Goodwill	165,103
Deferred income taxes	79,648
Noncurrent receivables	41,657
Other assets	51,136
Total assets	1,432,427
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable	51,373
Accrued liabilities	113,143
Current maturities of long-term debt	1,231
Income taxes payable	20,725
Total current liabilities	186,472
Long-term debt	529,003
Other noncurrent liabilities	92,218
Deferred taxes and other liabilities	12,863
Total liabilities	820,556
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	430,231
Retained earnings	583,694
Accumulated items of other comprehensive income:
Translation adjustments	(110,212)
Pension and postretirement liability adjustments	(48,293)
Derivative valuation adjustment	9,432
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	608,289
Noncontrolling interest	3,582
Total equity	611,871
Total liabilities and shareholders' equity	1,432,427
As adjusted to exclude adoption of ASC 606 [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock	37
As adjusted to exclude adoption of ASC 606 [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock	$ 3