Shareholders' Equity (Schedule of Activity in Shareholders' Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Beginning balance		$ 702,689	$ 608,280	$ 573,015
Beginning balance (in shares)		32,300,000	32,300,000
Net income		$ 97,243	$ 133,383	83,019
Compensation and benefits paid or payable in shares		622	1,311	1,437
Options exercised		55	112	201
Shares issued to Directors'		883	752	767
Cumulative translation adjustments		40,788	(6,886)	(28,675)
Pension and postretirement liability adjustments		10,333	(2,885)	3,427
Derivative valuation adjustment		(6,409)	$ (7,832)	$ 2,744
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Ending balance		$ 819,865	$ 702,689	$ 608,280
Ending balance (in shares)		32,300,000	32,300,000	32,300,000
Retained earnings		$ 770,746	$ 698,496
Cumulative Effect, Period of Adoption, Adjustment
Beginning balance		(1,443)	35	$ (5,395)
Ending balance			(1,443)	35
Retained earnings				100	$ 500
Common Class A
Dividends declared		$ (23,651)	(21,818)	$ (20,029)
Conversion of Class B shares to Class A shares			$ 2
Conversion of Class B shares to Class A shares (in shares)			1,616,000
Dividends declared per share amount (in dollars per share)		$ 0.77	$ 0.73	$ 0.69
Common Class B
Beginning balance (in shares)		1,617,998
Dividends declared		$ (1,245)	$ (1,763)	$ (2,231)
Conversion of Class B shares to Class A shares			$ (1)
Conversion of Class B shares to Class A shares (in shares)			(1,616,000)
Ending balance (in shares)		1,617,998	1,617,998
Dividends declared per share amount (in dollars per share)		$ 0.77	$ 0.73	$ 0.69
Common Class B | Standish Family Holdings, LLC
Conversion of stock (in shares)	1,600,000
Common Stock | Common Class A
Beginning balance		$ 39	$ 37	$ 37
Beginning balance (in shares)		39,099,000	37,450,000	37,396,000
Compensation and benefits paid or payable in shares (in shares)		13,000	26,000	44,000
Options exercised (in shares)		3,000	7,000	10,000
Ending balance		$ 39	$ 39	$ 37
Ending balance (in shares)		39,115,000	39,099,000	37,450,000
Common Stock | Series B Preferred Stock
Beginning balance		$ 2	$ 3	$ 3
Beginning balance (in shares)		1,618,000	3,234,000	3,234,000
Ending balance		$ 2	$ 2	$ 3
Ending balance (in shares)		1,618,000	1,618,000	3,234,000
Additional paid-in capital
Beginning balance		$ 432,518	$ 430,555	$ 428,423
Compensation and benefits paid or payable in shares		622	1,311	1,437
Options exercised		55	112	201
Shares issued to Directors'		501	540	494
Ending balance		433,696	432,518	430,555
Retained earnings
Beginning balance		698,496	589,645	534,082
Net income		98,589	132,398	82,891
Conversion of Class B shares to Class A shares			(1)
Ending balance		770,746	698,496	589,645
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Beginning balance		(1,443)	35	(5,068)
Ending balance			(1,443)	35
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment | ASC 606
Beginning balance				(5,600)
Retained earnings | Common Class A
Dividends declared		(23,651)	(21,818)	(20,029)
Retained earnings | Common Class B
Dividends declared		(1,245)	(1,763)	(2,231)
Accumulated items of other comprehensive income
Beginning balance		(175,981)	(158,388)	(135,901)
Cumulative translation adjustments		39,649	(6,876)	(28,658)
Pension and postretirement liability adjustments		10,333	(2,885)	3,427
Derivative valuation adjustment		(6,409)	(7,832)	2,744
Ending balance		(132,408)	(175,981)	(158,388)
Treasury Stock
Beginning balance		$ (256,391)	$ (256,603)	$ (256,876)
Beginning balance (in shares)		8,409,000	8,419,000	8,431,000
Shares issued to Directors'		$ 382	$ 212	$ 273
Shares issued to Directors' (in shares)		(18,000)	(10,000)	(12,000)
Ending balance		$ (256,009)	$ (256,391)	$ (256,603)
Ending balance (in shares)		8,391,000	8,409,000	8,419,000
Noncontrolling Interest
Beginning balance		$ 4,006	$ 3,031	$ 3,247
Net income		(1,346)	985	128
Cumulative translation adjustments		1,139	(10)	(17)
Ending balance		$ 3,799	$ 4,006	3,031
Noncontrolling Interest | Cumulative Effect, Period of Adoption, Adjustment
Beginning balance				(327)
Noncontrolling Interest | Cumulative Effect, Period of Adoption, Adjustment | ASC 606
Beginning balance				$ (300)