Revenue Recognition (Schedule of Consolidated Balance Sheet) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 151,426	$ 183,727	$ 143,333	$ 181,742
Accounts receivable, net	248,538	202,675
Contract assets	42,895
Inventories	100,034	136,519
Income taxes prepaid and receivable	6,132	6,266
Prepaid expenses and other current assets	18,675	14,520
Total current assets	567,700	543,707
Property, plant and equipment, net	459,388	454,302
Intangibles, net	53,881	55,441
Goodwill	168,311	166,796
Deferred income taxes	70,174	68,648
Noncurrent receivables	35,338	32,811
Other assets	45,543	39,493
Total assets	1,400,335	1,361,198
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable	226	262
Accounts payable	45,694	44,899
Accrued liabilities	122,103	105,914
Current maturities of long-term debt	1,821	1,799
Income taxes payable	5,182	8,643
Total current liabilities	175,026	161,517
Long-term debt	518,656	514,120
Other noncurrent liabilities	100,170	101,555
Deferred taxes and other liabilities	11,339	10,991
Total liabilities	805,191	788,183
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital	428,859	428,423
Retained earnings	533,759	534,082
Accumulated items of other comprehensive income:
Translation adjustments	(69,672)	(87,318)
Pension and postretirement liability adjustments	(50,549)	(50,536)
Derivative valuation adjustment	6,433	1,953
Treasury stock (Class A), at cost 8,431,335 shares in 2017 and 8,443,444 shares in 2016	(256,876)	(256,876)
Total Company shareholders' equity	591,994	569,768
Noncontrolling interest	3,150	3,247
Total equity	595,144	573,015
Total liabilities and shareholders' equity	1,400,335	1,361,198
Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock	37	37
Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock	$ 3	3
As previously reported [Member]
ASSETS
Cash and cash equivalents		183,727
Accounts receivable, net		202,675
Contract assets
Inventories		136,519
Income taxes prepaid and receivable		6,266
Prepaid expenses and other current assets		14,520
Total current assets		543,707
Property, plant and equipment, net		454,302
Intangibles, net		55,441
Goodwill		166,796
Deferred income taxes		68,648
Noncurrent receivables		32,811
Other assets		39,493
Total assets		1,361,198
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable		262
Accounts payable		44,899
Accrued liabilities		105,914
Current maturities of long-term debt		1,799
Income taxes payable		8,643
Total current liabilities		161,517
Long-term debt		514,120
Other noncurrent liabilities		101,555
Deferred taxes and other liabilities		10,991
Total liabilities		788,183
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital		428,423
Retained earnings		534,082
Accumulated items of other comprehensive income:
Translation adjustments		(87,318)
Pension and postretirement liability adjustments		(50,536)
Derivative valuation adjustment		1,953
Treasury stock (Class A), at cost 8,431,335 shares in 2017 and 8,443,444 shares in 2016		(256,876)
Total Company shareholders' equity		569,768
Noncontrolling interest		3,247
Total equity		573,015
Total liabilities and shareholders' equity		1,361,198
As previously reported [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock		37
As previously reported [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock		3
Adjustments Increase/(decrease) [Member]
ASSETS
Cash and cash equivalents
Accounts receivable, net		10,210
Contract assets		44,872
Inventories		(47,054)
Income taxes prepaid and receivable
Prepaid expenses and other current assets
Total current assets		8,028
Property, plant and equipment, net
Intangibles, net
Goodwill
Deferred income taxes		1,756
Noncurrent receivables
Other assets		1,119
Total assets		10,903
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable
Accounts payable
Accrued liabilities		16,808
Current maturities of long-term debt
Income taxes payable
Total current liabilities		16,808
Long-term debt
Other noncurrent liabilities
Deferred taxes and other liabilities		52
Total liabilities		16,860
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital
Retained earnings		(5,630)
Accumulated items of other comprehensive income:
Translation adjustments
Pension and postretirement liability adjustments
Derivative valuation adjustment
Treasury stock (Class A), at cost 8,431,335 shares in 2017 and 8,443,444 shares in 2016
Total Company shareholders' equity		(5,630)
Noncontrolling interest		(327)
Total equity		(5,957)
Total liabilities and shareholders' equity		10,903
Adjustments Increase/(decrease) [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock
Adjustments Increase/(decrease) [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock
Opening balance, as adjusted, January 1, 2018 [Member]
ASSETS
Cash and cash equivalents		183,727
Accounts receivable, net		212,885
Contract assets		44,872
Inventories		89,465
Income taxes prepaid and receivable		6,266
Prepaid expenses and other current assets		14,520
Total current assets		551,735
Property, plant and equipment, net		454,302
Intangibles, net		55,441
Goodwill		166,796
Deferred income taxes		70,404
Noncurrent receivables		32,811
Other assets		40,612
Total assets		1,372,101
LIABILITIES AND SHAREHOLDERS' EQUITY
Notes and loans payable		262
Accounts payable		44,899
Accrued liabilities		122,722
Current maturities of long-term debt		1,799
Income taxes payable		8,643
Total current liabilities		178,325
Long-term debt		514,120
Other noncurrent liabilities		101,555
Deferred taxes and other liabilities		11,043
Total liabilities		805,043
SHAREHOLDERS' EQUITY
Preferred stock, par value $5.00 per share; authorized 2,000,000 shares; none issued
Additional paid in capital		428,423
Retained earnings		528,452
Accumulated items of other comprehensive income:
Translation adjustments		(87,318)
Pension and postretirement liability adjustments		(50,536)
Derivative valuation adjustment		1,953
Treasury stock (Class A), at cost 8,431,335 shares in 2017 and 8,443,444 shares in 2016		(256,876)
Total Company shareholders' equity		564,138
Noncontrolling interest		2,920
Total equity		567,058
Total liabilities and shareholders' equity		1,372,101
Opening balance, as adjusted, January 1, 2018 [Member] | Common Class A [Member]
SHAREHOLDERS' EQUITY
Common Stock		37
Opening balance, as adjusted, January 1, 2018 [Member] | Common Class B [Member]
SHAREHOLDERS' EQUITY
Common Stock		$ 3