Changes in Shareholders' Equity (Schedule of Activity in Shareholders' Equity) (Details) - USD ($)	3 Months Ended								9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019		Sep. 30, 2020		Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 706,158,000	$ 669,561,000	$ 702,689,000		$ 651,316,000	$ 626,407,000	$ 608,280,000		$ 702,689,000		$ 608,280,000
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member				us-gaap:AccountingStandardsUpdate201602Member		us-gaap:AccountingStandardsUpdate201613Member
Net income	29,590,000	32,449,000	$ 7,594,000		40,125,000	34,259,000	$ 29,408,000		$ 69,633,000		103,792,000
Compensation and benefits paid or payable in shares	80,000	783,000	(682,000)		790,000	1,170,000	(547,000)
Options exercised	5,000	20,000	0		33,000	28,000	44,000
Shares issued to Directors		416,000
Dividends declared	(5,837,000)	(5,835,000)	(5,834,000)		(5,524,000)	(5,523,000)	(5,231,000)
Dividends declared Class B	(307,000)	(307,000)	(307,000)		(291,000)	(291,000)	(582,000)
Cumulative translation adjustments	20,022,000	9,116,000	(25,638,000)		(22,535,000)	1,000	(662,000)
Pension and postretirement liability adjustments	(474,000)	142,000	890,000		490,000	(40,000)	(1,487,000)
Derivative valuation adjustment	621,000	(187,000)	(7,708,000)		(1,323,000)	(4,695,000)	(2,851,000)
Ending balance	749,858,000	706,158,000	669,561,000		663,081,000	651,316,000	626,407,000		749,858,000		663,081,000
Revision of Prior Period, Adjustment [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(1,443,000)	[1]			35,000	[2]	(1,443,000)	[1]	35,000	[2]
Common Stock [Member] | Common Class A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 39,000	$ 39,000	$ 39,000		$ 39,000	$ 37,000	$ 37,000		$ 39,000		$ 37,000
Beginning balance (in shares)	39,113,000	39,112,000	39,099,000		39,096,000	37,478,000	37,450,000		39,099,000		37,450,000
Compensation and benefits paid or payable in shares							$ 25,000
Compensation and benefits paid or payable in shares (in shares)			13,000
Options exercised (in shares)		1,000			2,000	2,000	3,000
Conversion of Class B shares to Class A shares (in shares)						1,616,000
Conversion of Class B shares to Class A shares						$ 2,000
Ending balance	$ 39,000	$ 39,000	$ 39,000		$ 39,000	$ 39,000	$ 37,000		$ 39,000		$ 39,000
Ending balance (in shares)	39,113,000	39,113,000	39,112,000		39,098,000	39,096,000	37,478,000		39,113,000		39,098,000
Common Stock [Member] | Common Class B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 2,000	$ 2,000	$ 2,000		$ 2,000	$ 3,000	$ 3,000		$ 2,000		$ 3,000
Beginning balance (in shares)	1,618,000	1,618,000	1,618,000		1,618,000	3,234,000	3,234,000		1,618,000		3,234,000
Conversion of Class B shares to Class A shares (in shares)						(1,616,000)
Conversion of Class B shares to Class A shares						$ (1,000)
Ending balance	$ 2,000	$ 2,000	$ 2,000		$ 2,000	$ 2,000	$ 3,000		$ 2,000		$ 2,000
Ending balance (in shares)	1,618,000	1,618,000	1,618,000		1,618,000	1,618,000	3,234,000		1,618,000		1,618,000
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 432,738,000	$ 431,836,000	$ 432,518,000		$ 431,037,000	$ 430,052,000	$ 430,555,000		$ 432,518,000		$ 430,555,000
Compensation and benefits paid or payable in shares	80,000	466,000	(682,000)		790,000	958,000	(547,000)
Options exercised	5,000	20,000			33,000	28,000	44,000
Shares issued to Directors		416,000
Conversion of Class B shares to Class A shares						(1,000)
Ending balance	432,823,000	432,738,000	431,836,000		431,860,000	431,037,000	430,052,000		432,823,000		431,860,000
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	726,233,000	700,021,000	698,496,000		641,297,000	613,057,000	589,645,000		698,496,000		589,645,000
Net income	29,589,000	32,354,000	9,109,000		40,009,000	34,054,000	29,190,000
Ending balance	749,678,000	726,233,000	700,021,000		675,491,000	641,297,000	613,057,000		749,678,000		675,491,000
Retained Earnings [Member] | Revision of Prior Period, Adjustment [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(1,443,000)	[1]			35,000	[2]	(1,443,000)	[1]	35,000	[2]
Retained Earnings [Member] | Common Class A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(5,837,000)	(5,835,000)	(5,834,000)		(5,524,000)	(5,523,000)	(5,231,000)
Retained Earnings [Member] | Common Class B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared Class B	(307,000)	(307,000)	(307,000)		(291,000)	(291,000)	(582,000)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(199,627,000)	(208,546,000)	(175,981,000)		(168,116,000)	(163,380,000)	(158,388,000)		(175,981,000)		(158,388,000)
Cumulative translation adjustments	19,821,000	8,964,000	(25,747,000)		(22,522,000)	(1,000)	(654,000)
Pension and postretirement liability adjustments	(474,000)	142,000	890,000		490,000	(40,000)	(1,487,000)
Derivative valuation adjustment	621,000	(187,000)	(7,708,000)		(1,323,000)	(4,695,000)	(2,851,000)
Ending balance	(179,659,000)	(199,627,000)	(208,546,000)		(191,471,000)	(168,116,000)	(163,380,000)		(179,659,000)		(191,471,000)
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (256,074,000)	$ (256,391,000)	$ (256,391,000)		$ (256,391,000)	$ (256,603,000)	$ (256,603,000)		$ (256,391,000)		$ (256,603,000)
Beginning balance (in shares)	8,394	8,409	8,409		8,409	8,419	8,419		8,409		8,419
Compensation and benefits paid or payable in shares		$ 317,000				$ 212,000
Compensation and benefits paid or payable in shares (in shares)		(15)				(10)
Ending balance	$ (256,074,000)	$ (256,074,000)	$ (256,391,000)		$ (256,391,000)	$ (256,391,000)	$ (256,603,000)		$ (256,074,000)		$ (256,391,000)
Ending balance (in shares)	8,394	8,394	8,409		8,409	8,409	8,419		8,394		8,409
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 2,847,000	$ 2,600,000	$ 4,006,000		$ 3,448,000	$ 3,241,000	$ 3,031,000		$ 4,006,000		$ 3,031,000
Net income	1,000	95,000	(1,515,000)		116,000	205,000	218,000
Cumulative translation adjustments	201,000	152,000	109,000		(13,000)	2,000	(8,000)
Ending balance	$ 3,049,000	$ 2,847,000	$ 2,600,000		$ 3,551,000	$ 3,448,000	$ 3,241,000		$ 3,049,000		$ 3,551,000

[1] As described in Note 1, the Company adopted the provisions of ASC 326, Current Expected Credit Losses (CECL) effective January 1, 2020, which resulted in a decrease to Retained earnings of $1.4 million.

[2] The Company adopted ASC 842, Leases effective January 1, 2019, which resulted in an increase to Retained earnings of less than $0.1 million.