Revenue Recognition (Schedule of Consolidated Balance Sheet) (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 8,431,335 shares in 2017 and 8,443,444 shares in 2016	(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 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			7,667
Contract assets			47,415
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			210,342
Contract assets			47,415
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