Changes in Shareholders' Equity (Schedule of Activity in Shareholders' Equity) (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Balance	$ 651,316	$ 626,407	$ 608,280	$ 588,630	$ 592,578	$ 573,015	$ 608,280	$ 573,015
Adoption of accounting standards			35			(5,395)
Net income	40,125	34,259	29,408	28,005	29,843	7,899	103,792	65,747
Compensation and benefits paid or payable in shares	790	1,170	(547)	543	1,047	289
Options exercised	33	28	44	52	3	147
Dividends declared Class A	(5,524)	(5,523)	(5,231)	(4,935)	(4,935)	(4,933)
Dividends declared Class B	(291)	(291)	(582)	(550)	(550)	(550)
Cumulative translation adjustments	(22,535)	1	(662)	(8,017)	(33,205)	17,639
Pension and postretirement liability adjustments	490	(40)	(1,487)	129	2,127	(13)
Derivative valuation adjustment	(1,323)	(4,695)	(2,851)	1,277	1,722	4,480
Balance	663,081	651,316	626,407	605,134	588,630	592,578	663,081	605,134
Common Class A [Member]
Balance	$ 39	$ 37	$ 37	$ 37	$ 37	$ 37	$ 37	$ 37
Balance, Shares	39,096	37,478	37,450	37,448	37,448	37,396	37,450	37,396
Compensation and benefits paid or payable in shares			$ 25			$ 44
Options exercised	$ 2	$ 2	3	$ 2		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	$ 39	$ 37	$ 37	$ 37	$ 37	$ 39	$ 37
Balance, Shares	39,098	39,096	37,478	37,450	37,448	37,448	39,098	37,450
Common Class B [Member]
Balance	$ 2	$ 3	$ 3	$ 3	$ 3	$ 3	$ 3	$ 3
Balance, Shares	1,618	3,234	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	$ 2	$ 3	$ 3	$ 3	$ 3	$ 2	$ 3
Balance, Shares	1,618	1,618	3,234	3,234	3,234	3,234	1,618	3,234
Additional paid in capital [Member]
Balance	$ 431,037	$ 430,052	$ 430,555	$ 429,635	$ 428,859	$ 428,423	$ 430,555	$ 428,423
Compensation and benefits paid or payable in shares	790	958	(547)	544	773	289
Options exercised	33	28	44	52	3	147
Conversion of Class B shares to Class A shares, rounding		(1)
Balance	431,860	431,037	430,052	430,231	429,635	428,859	431,860	430,231
Retained earnings [Member]
Balance	641,297	613,057	589,645	555,610	531,193	534,082	589,645	534,082
Adoption of accounting standards			35			(5,068)
Net income	34,054		29,190	27,736	29,902	7,662
Balance	675,491	641,297	613,057	577,861	555,610	531,193	675,491	577,861
Retained earnings [Member] | Common Class A [Member]
Dividends declared Class A	(5,524)	(5,523)	(5,231)	(4,935)	(4,935)	(4,933)
Retained earnings [Member] | Common Class B [Member]
Dividends declared Class B	(291)	(291)	(582)	(550)	(550)	(550)
Total Other Comprehensive Income [Member]
Balance	(168,116)	(163,380)	(158,388)	(143,155)	(113,788)	(135,901)	(158,388)	(135,901)
Cumulative translation adjustments	(22,522)	(1)	(654)	(8,012)	(33,216)	17,646
Pension and postretirement liability adjustments	490	(40)	(1,487)	129	2,127	(13)
Derivative valuation adjustment	(1,323)	(4,695)	(2,851)	1,277	1,722	4,480
Balance	191,471	(168,116)	(163,380)	(149,761)	(143,155)	(113,788)	191,471	(149,761)
Treasury stock [Member] | Common Class A [Member]
Balance	$ (256,391)	$ (256,603)	$ (256,603)	$ (256,602)	$ (256,876)	$ (256,876)	$ (256,603)	$ (256,876)
Balance, Shares	8,409	8,419	8,419	8,419	8,431	8,431	8,419	8,431
Compensation and benefits paid or payable in shares		$ 212		$ (1)	$ 274
Compensation and benefits paid or payable in shares, Shares		(10)
Shares issued to Directors					(12)
Balance	$ (256,391)	$ (256,391)	$ (256,603)	$ (256,603)	$ (256,602)	$ (256,876)	$ (256,391)	$ (256,603)
Balance, Shares	8,409	8,409	8,419	8,419	8,419	8,431	8,409	8,419
Noncontrolling Interest [Member]
Balance	$ 3,448	$ 3,241	$ 3,031	$ 3,102	$ 3,150	$ 3,247	$ 3,031	$ 3,247
Adoption of accounting standards						(327)
Net income	116	205	218	269	(59)	237
Cumulative translation adjustments	(13)	2	(8)	(5)	11	(7)
Balance	$ 3,551	$ 3,448	$ 3,241	$ 3,366	$ 3,102	$ 3,150	$ 3,551	$ 3,366