Changes in Shareholders' Equity (Schedule of Activity in Shareholders' Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 819,865	$ 702,689
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Net income	27,609	7,594
Compensation and benefits paid or payable in shares	(13)	(682)
Options exercised	128	0
Shares issued to Directors'	0	0
Cumulative translation adjustments	(16,165)	(25,638)
Pension and postretirement liability adjustments	509	890
Derivative valuation adjustment	752	(7,708)
Balance at end of the period	$ 826,211	$ 669,561	$ 702,689
Dividends declared per share, Class A and Class B (in dollars per share)	$ 0.20	$ 0.19
Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Options exercised (in shares)	6,000	0
Dividends declared	$ (6,150)	$ (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	$ 0.19
Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at the beginning of the period (in shares)	1,617,998
Dividends declared	$ (324)	$ (307)
Balance at end of the period		$ 2
Balance at the end of the period (in shares)	1,617,998	1,618,000
Dividends declared per share, Class A and Class B (in dollars per share)	$ 0.20	$ 0.19
Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period		$ (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
Balance at the beginning of the period (in shares)	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
Balance at the end of the period (in shares)	39,141,000		39,099,000
Common Stock | Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 2	$ 2
Balance at the beginning of the period (in shares)	1,618,000	1,618,000
Balance at end of the period	$ 2		$ 2
Balance at the end of the period (in shares)	1,618,000		1,618,000
Additional paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 433,696	$ 432,518
Compensation and benefits paid or payable in shares	(13)	(682)
Options exercised	128	0
Balance at end of the period	433,811	431,836	$ 432,518
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	770,746	698,496
Net income	27,582	9,109
Balance at end of the period	791,854	700,021	698,496
Retained earnings | Common Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(6,150)	(5,834)
Retained earnings | Common Class B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(324)	(307)
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	(1,400)	(1,443)
Balance at end of the period			(1,443)
Accumulated items of other comprehensive income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	(132,408)	(175,981)
Cumulative translation adjustments	(15,955)	(25,747)
Pension and postretirement liability adjustments	509	890
Derivative valuation adjustment	752	(7,708)
Balance at end of the period	(147,102)	(208,546)	(175,981)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ (256,009)	$ (256,391)
Balance at the beginning of the period (in shares)	8,391,000	8,409,000
Balance at end of the period	$ (256,009)	$ (256,391)	$ (256,391)
Balance at the end of the period (in shares)	8,391,000	8,409,000	8,409,000
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of the period	$ 3,799	$ 4,006
Net income	27	(1,515)
Cumulative translation adjustments	(210)	109
Balance at end of the period	$ 3,616	$ 2,600	$ 4,006