Changes in Shareholders' Equity (Schedule of Activity in Shareholders' Equity) (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Balance	$ 626,407	$ 608,280	$ 592,578	$ 573,015	$ 608,280	$ 573,015
Adoption of accounting standards		35		(5,395)
Net income	34,259	29,408	29,843	7,899	63,667	37,742
Compensation and benefits paid or payable in shares	1,170	(547)	1,047	289
Options exercised	28	44	3	147
Dividends declared Class A	(5,523)	(5,231)	(4,935)	(4,933)
Dividends declared Class B	(291)	(582)	(550)	(550)
Cumulative translation adjustments	1	(662)	(33,205)	17,639
Pension and postretirement liability adjustments	(40)	(1,487)	2,127	(13)
Derivative valuation adjustment	(4,695)	(2,851)	1,722	4,480
Balance	651,316	626,407	588,630	592,578	651,316	588,630
Common Class A [Member]
Balance	$ 37	$ 37	$ 37	$ 37	$ 37	$ 37
Balance, Shares	37,478	37,450	37,448	37,396	37,450	37,396
Compensation and benefits paid or payable in shares		$ 25		$ 44
Options exercised	$ 2	3		8
Conversion of Class B shares to Class A shares, rounding	$ 2
Conversion of Class B shares to Class A shares, rounding, Shares	1,616
Balance	$ 39	$ 37	$ 37	$ 37	$ 39	$ 37
Balance, Shares	39,096	37,478	37,448	37,448	39,096	37,448
Common Class B [Member]
Balance	$ 3		$ 3	$ 3		$ 3
Balance, Shares	3,234	3,234	3,234	3,234	3,234	3,234
Conversion of Class B shares to Class A shares, rounding	$ (1)
Conversion of Class B shares to Class A shares, rounding, Shares	(1,616)
Balance	$ 2	$ 3	$ 3	$ 3	$ 2	$ 3
Balance, Shares	1,618	3,234	3,234	3,234	1,618	3,234
Additional paid in capital [Member]
Balance	$ 430,052	$ 430,555	$ 428,859	$ 428,423	$ 430,555	$ 428,423
Compensation and benefits paid or payable in shares	958	(547)	773	289
Options exercised	28	44	3	147
Conversion of Class B shares to Class A shares, rounding	(1)
Balance	431,037	430,052	429,635	428,859	431,037	429,635
Retained earnings [Member]
Balance	613,057	589,645	531,193	534,082	589,645	534,082
Adoption of accounting standards		35		(5,068)
Net income	34,054	29,190	29,902	7,662
Balance	641,297	613,057	555,610	531,193	641,297	555,610
Retained earnings [Member] | Common Class A [Member]
Dividends declared Class A	(5,523)	(5,231)	(4,935)	(4,933)
Retained earnings [Member] | Common Class B [Member]
Dividends declared Class B	(291)	(582)	(550)	(550)
Total Other Comprehensive Income [Member]
Balance	(163,380)	(158,388)	(113,788)	(135,901)	(158,388)	(135,901)
Cumulative translation adjustments	(1)	(654)	(33,216)	17,646
Pension and postretirement liability adjustments	(40)	(1,487)	2,127	(13)
Derivative valuation adjustment	(4,695)	(2,851)	1,722	4,480
Balance	(168,116)	(163,380)	(143,155)	(113,788)	(168,116)	(143,155)
Treasury stock [Member] | Common Class A [Member]
Balance	$ (256,603)	$ (256,603)	$ (256,876)	$ (256,876)	$ (256,603)	$ (256,876)
Balance, Shares	8,419	8,419	8,431	8,431	8,419	8,431
Compensation and benefits paid or payable in shares	$ 212		$ 274
Compensation and benefits paid or payable in shares, Shares	(10)
Shares issued to Directors			12
Balance	$ (256,391)	$ (256,603)	$ (256,602)	$ (256,876)	$ (256,391)	$ (256,602)
Balance, Shares	8,409	8,419	8,419	8,431	8,409	8,419
Noncontrolling Interest [Member]
Balance	$ 3,241	$ 3,031	$ 3,150	$ 3,247	$ 3,031	$ 3,247
Adoption of accounting standards				(327)
Net income	205	218	(59)	237
Cumulative translation adjustments	2	(8)	11	(7)
Balance	$ 3,448	$ 3,241	$ 3,102	$ 3,150	$ 3,448	$ 3,102