Changes in Shareholders' Equity (Schedule of Activity in Shareholders' Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 826,211	$ 819,865	$ 669,561	$ 702,689	$ 819,865	$ 702,689
Accounting Standards Update [Extensible Enumeration]							us-gaap:AccountingStandardsUpdate201613Member
Net income	31,440	27,609	32,449	7,594	59,050	40,043
Compensation and benefits paid or payable in shares	692	(13)	466	(682)
Options exercised	21	128	20
Shares issued to Directors'	947		733
Cumulative translation adjustments	13,957	(16,165)	9,116	(25,638)
Pension and postretirement liability adjustments	(130)	509	142	890
Derivative valuation adjustment	1,394	752	(187)	(7,708)
Balance at end of the period	$ 868,059	$ 826,211	$ 706,158	669,561	$ 868,059	$ 706,158	$ 702,689
Dividends declared per share, Class A and Class B (in dollars per share)	$ 0.20		$ 0.19		$ 0.40	$ 0.38
Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period			$ 39
Balance at the beginning of the period (in shares)			39,112,000
Options exercised (in shares)	1,000	6,000	1,000
Dividends declared	$ (6,150)	$ (6,150)	$ (5,835)	(5,834)
Balance at end of the period				$ 39
Balance at the end of the period (in shares)				39,112,000
Dividends declared per share, Class A and Class B (in dollars per share)	$ 0.20	$ 0.20	$ 0.19	$ 0.19
Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period			$ 2
Balance at the beginning of the period (in shares)		1,617,998	1,618,000		1,617,998
Dividends declared	$ (323)	$ (324)	$ (307)	$ (307)
Balance at end of the period				$ 2
Balance at the end of the period (in shares)	1,617,998			1,618,000	1,617,998
Dividends declared per share, Class A and Class B (in dollars per share)	$ 0.20	$ 0.20	$ 0.19	$ 0.19
Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period				$ (1,443)		$ (1,443)
Balance at end of the period							(1,443)
Common Stock | Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 39	$ 39		$ 39	$ 39	$ 39
Balance at the beginning of the period (in shares)	39,141,000	39,115,000		39,099,000	39,115,000	39,099,000
Compensation and benefits paid or payable in shares (in shares)		20,000		13,000
Balance at end of the period	$ 39	$ 39	$ 39		$ 39	$ 39	$ 39
Balance at the end of the period (in shares)	39,142,000	39,141,000	39,113,000		39,142,000	39,113,000	39,099,000
Common Stock | Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 2	$ 2		$ 2	$ 2	$ 2
Balance at the beginning of the period (in shares)	1,618,000	1,618,000		1,618,000	1,618,000	1,618,000
Balance at end of the period	$ 2	$ 2	$ 2		$ 2	$ 2	$ 2
Balance at the end of the period (in shares)	1,618,000	1,618,000	1,618,000		1,618,000	1,618,000	1,618,000
Additional paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 433,811	$ 433,696	$ 431,836	$ 432,518	$ 433,696	$ 432,518
Compensation and benefits paid or payable in shares	692	(13)	466	(682)
Options exercised	21	128	20
Shares issued to Directors'	706		416
Balance at end of the period	435,230	433,811	432,738	431,836	435,230	432,738	$ 432,518
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	791,854	770,746	700,021	698,496	770,746	698,496
Net income	31,397	27,582	32,354	9,109
Balance at end of the period	816,778	791,854	726,233	700,021	816,778	726,233	698,496
Retained earnings | Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(6,150)	(6,150)	(5,835)	(5,834)
Retained earnings | Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(323)	(324)	(307)	(307)
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period				(1,443)		(1,443)
Balance at end of the period							(1,443)
Accumulated other comprehensive income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	(147,102)	(132,408)	(208,546)	(175,981)	(132,408)	(175,981)
Cumulative translation adjustments	13,774	(15,955)	8,964	(25,747)
Pension and postretirement liability adjustments	(130)	509	142	890
Derivative valuation adjustment	1,394	752	(187)	(7,708)
Balance at end of the period	(132,064)	(147,102)	(199,627)	(208,546)	(132,064)	(199,627)	(175,981)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ (256,009)	$ (256,009)	$ (256,391)	$ (256,391)	$ (256,009)	$ (256,391)
Balance at the beginning of the period (in shares)	8,391,000	8,391,000	8,409,000	8,409,000	8,391,000	8,409,000
Shares issued to Directors' (in shares)	(11,000)		(15,000)
Shares issued to Directors'	$ 241		$ 317
Balance at end of the period	$ (255,768)	$ (256,009)	$ (256,074)	$ (256,391)	$ (255,768)	$ (256,074)	$ (256,391)
Balance at the end of the period (in shares)	8,380,000	8,391,000	8,394,000	8,409,000	8,380,000	8,394,000	8,409,000
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 3,616	$ 3,799	$ 2,600	$ 4,006	$ 3,799	$ 4,006
Net income	43	27	95	(1,515)
Cumulative translation adjustments	183	(210)	152	109
Balance at end of the period	$ 3,842	$ 3,616	$ 2,847	$ 2,600	$ 3,842	$ 2,847	$ 4,006