Changes in Shareholders' Equity (Schedule of Activity in Shareholders' Equity) (Details) - USD ($)	3 Months Ended						6 Months Ended				12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020		Jun. 30, 2019	Mar. 31, 2019		Jun. 30, 2020		Jun. 30, 2019		Dec. 31, 2019		Dec. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 669,561,000	$ 702,689,000		$ 626,407,000	$ 608,280,000		$ 702,689,000		$ 608,280,000		$ 608,280,000
Accounting Standards Update [Extensible List]							us-gaap:AccountingStandardsUpdate201613Member				us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201602Member
Net income	32,449,000	7,594,000		34,259,000	29,408,000		$ 40,043,000		63,667,000
Compensation and benefits paid or payable in shares	783,000	(682,000)		1,170,000	(547,000)
Options exercised	20,000	0		28,000	44,000
Shares issued to Directors	416,000
Dividends declared	(5,835,000)	(5,834,000)		(5,523,000)	(5,231,000)
Dividends declared Class B	(307,000)	(307,000)		(291,000)	(582,000)
Cumulative translation adjustments	9,116,000	(25,638,000)		1,000	(662,000)
Pension and postretirement liability adjustments	142,000	890,000		(40,000)	(1,487,000)
Derivative valuation adjustment	(187,000)	(7,708,000)		(4,695,000)	(2,851,000)
Ending balance	706,158,000	669,561,000		651,316,000	626,407,000		706,158,000		651,316,000		$ 702,689,000		$ 608,280,000
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]	35,000	[2]
Ending balance											(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		$ 37,000	$ 37,000		$ 39,000		$ 37,000		$ 37,000
Beginning balance (in shares)	39,112,000	39,099,000		37,478,000	37,450,000		39,099,000		37,450,000		37,450,000
Compensation and benefits paid or payable in shares					$ 25,000
Compensation and benefits paid or payable in shares (in shares)	0	13,000		0
Options exercised					3,000
Shares issued to Directors (in shares)	0	0		0
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	$ 37,000		$ 39,000		$ 39,000		$ 39,000		$ 37,000
Ending balance (in shares)	39,113,000	39,112,000		39,096,000	37,478,000		39,113,000		39,096,000		39,099,000		37,450,000
Common Stock [Member] | Common Class B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 2,000	$ 2,000		$ 3,000	$ 3,000		$ 2,000		$ 3,000		$ 3,000
Beginning balance (in shares)	1,618,000	1,618,000		3,234,000	3,234,000		1,618,000		3,234,000		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	$ 3,000		$ 2,000		$ 2,000		$ 2,000		$ 3,000
Ending balance (in shares)	1,618,000	1,618,000		1,618,000	3,234,000		1,618,000		1,618,000		1,618,000		3,234,000
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 431,836,000	$ 432,518,000		$ 430,052,000	$ 430,555,000		$ 432,518,000		$ 430,555,000		$ 430,555,000
Compensation and benefits paid or payable in shares	466,000	(682,000)		958,000	(547,000)
Options exercised	20,000			28,000	44,000
Shares issued to Directors	416,000
Conversion of Class B shares to Class A shares				(1,000)
Ending balance	432,738,000	431,836,000		431,037,000	430,052,000		432,738,000		431,037,000		432,518,000		$ 430,555,000
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	700,021,000	698,496,000		613,057,000	589,645,000		698,496,000		589,645,000		589,645,000
Net income	32,354,000	9,109,000		34,054,000	29,190,000
Ending balance	726,233,000	700,021,000		641,297,000	613,057,000		726,233,000		641,297,000		698,496,000		589,645,000
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]	35,000	[2]
Ending balance											(1,443,000)	[1]	35,000	[2]
Retained Earnings [Member] | Common Class A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(5,835,000)	(5,834,000)		(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)		(291,000)	(582,000)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(208,546,000)	(175,981,000)		(163,380,000)	(158,388,000)		(175,981,000)		(158,388,000)		(158,388,000)
Cumulative translation adjustments	8,964,000	(25,747,000)		(1,000)	(654,000)
Pension and postretirement liability adjustments	142,000	890,000		(40,000)	(1,487,000)
Derivative valuation adjustment	(187,000)	(7,708,000)		(4,695,000)	(2,851,000)
Ending balance	(199,627,000)	(208,546,000)		(168,116,000)	(163,380,000)		(199,627,000)		(168,116,000)		(175,981,000)		(158,388,000)
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (256,391,000)	$ (256,391,000)		$ (256,603,000)	$ (256,603,000)		$ (256,391,000)		$ (256,603,000)		$ (256,603,000)
Beginning balance (in shares)	8,409	8,409		8,419	8,419		8,409		8,419		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)	$ (256,391,000)		$ (256,391,000)	$ (256,603,000)		$ (256,074,000)		$ (256,391,000)		$ (256,391,000)		$ (256,603,000)
Ending balance (in shares)	8,394	8,409		8,409	8,419		8,394		8,409		8,409		8,419
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 2,600,000	$ 4,006,000		$ 3,241,000	$ 3,031,000		$ 4,006,000		$ 3,031,000		$ 3,031,000
Net income	95,000	(1,515,000)		205,000	218,000
Cumulative translation adjustments	152,000	109,000		2,000	(8,000)
Ending balance	$ 2,847,000	$ 2,600,000		$ 3,448,000	$ 3,241,000		$ 2,847,000		$ 3,448,000		$ 4,006,000		$ 3,031,000

[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.