Revenue Recognition (Schedule of Consolidated Balance Sheets) (Details) - 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
Income taxes receivable and deferred	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
As reported [Member]
ASSETS
Cash and cash equivalents	154,744
Accounts receivable, net	249,482
Contract assets	59,244
Inventories	97,659
Income taxes prepaid and receivable	6,087
Prepaid expenses and other current assets	19,559
Total current assets	586,775
Property, plant and equipment, net	450,694
Intangibles, net	52,322
Goodwill	165,474
Income taxes receivable and deferred	81,237
Noncurrent receivables	36,981
Other assets	48,978
Total assets	1,422,461
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable	26
Accounts payable	54,752
Accrued liabilities	125,255
Current maturities of long-term debt	1,844
Income taxes payable	14,620
Total current liabilities	196,497
Long-term debt	523,186
Other noncurrent liabilities	97,563
Deferred taxes and other liabilities	13,556
Total liabilities	830,802
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	429,635
Retained earnings	558,639
Accumulated items of other comprehensive income:
Translation adjustments	(102,888)
Pension and postretirement liability adjustments	(48,422)
Derivative valuation adjustment	8,155
Treasury stock (Class A), at cost 8,418,620 shares in 2018 and 8,431,335 shares in 2017	(256,602)
Total Company shareholders' equity	588,557
Noncontrolling interest	3,102
Total equity	591,659
Total liabilities and shareholders' equity	1,422,461
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	(4,286)
Contract assets	(59,244)
Inventories	51,736
Income taxes prepaid and receivable
Prepaid expenses and other current assets
Total current assets	(11,794)
Property, plant and equipment, net
Intangibles, net
Goodwill
Income taxes receivable and deferred	(648)
Noncurrent receivables
Other assets	(1,256)
Total assets	(13,698)
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable
Accrued liabilities	(17,485)
Current maturities of long-term debt
Income taxes payable
Total current liabilities	(17,485)
Long-term debt
Other noncurrent liabilities
Deferred taxes and other liabilities	(52)
Total liabilities	(17,537)
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital
Retained earnings	3,065
Accumulated items of other comprehensive income:
Translation adjustments	531
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	3,596
Noncontrolling interest	243
Total equity	3,839
Total liabilities and shareholders' equity	(13,698)
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	154,744
Accounts receivable, net	245,196
Contract assets
Inventories	149,395
Income taxes prepaid and receivable	6,087
Prepaid expenses and other current assets	19,559
Total current assets	574,981
Property, plant and equipment, net	450,694
Intangibles, net	52,322
Goodwill	165,474
Income taxes receivable and deferred	80,589
Noncurrent receivables	36,981
Other assets	47,722
Total assets	1,408,763
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable	26
Accounts payable	54,752
Accrued liabilities	107,770
Current maturities of long-term debt	1,844
Income taxes payable	14,620
Total current liabilities	179,012
Long-term debt	523,186
Other noncurrent liabilities	97,563
Deferred taxes and other liabilities	13,504
Total liabilities	813,265
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	429,635
Retained earnings	561,704
Accumulated items of other comprehensive income:
Translation adjustments	(102,357)
Pension and postretirement liability adjustments	(48,422)
Derivative valuation adjustment	8,155
Treasury stock (Class A), at cost 8,418,620 shares in 2018 and 8,431,335 shares in 2017	(256,602)
Total Company shareholders' equity	592,153
Noncontrolling interest	3,345
Total equity	595,498
Total liabilities and shareholders' equity	1,408,763
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