Consolidated Statements of Changes in Common Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment	AOCI Attributable to Parent [Member]	AOCI Attributable to Parent [Member] Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock [Member]	Noncontrolling Interest [Member]	Class A Common Stock [Member]	Class B Common Stock [Member]
As of at Dec. 31, 2017	$ 2,915,145	$ 6,923	$ 370,700	$ 5,791,724	$ 201,812	$ 535,555	$ (194,889)	$ (3,802,834)	$ 0	$ 964	$ 19,036
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the year	271,408			271,408
Net income attributable to redeemable noncontrolling interests	(202)			(202)
Change in redemption value of redeemable noncontrolling interests	413		413
Dividends paid on common stock	(28,617)			(28,617)
Repurchase of Class B common stock	(118,030)							(118,030)
Issuance of Class B common stock, net of restricted stock award forfeitures	(1,485)		(340)					(1,145)
Amortization of unearned stock compensation and stock option expense	8,064		8,064
Other comprehensive income (loss), net of income taxes	(136,837)					(136,837)
Other	0
As of at Dec. 31, 2018	2,916,782		378,837	6,236,125		203,829		(3,922,009)	0	964	19,036
As of at Dec. 31, 2017	4,607
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income attributable to redeemable noncontrolling interests	202
Change in redemption value of redeemable noncontrolling interests	(413)
Other	(50)
As of at Dec. 31, 2018	4,346
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the year	327,879			327,879
Issuance of noncontrolling interest	6,556								6,556
Net loss attributable to noncontrolling interest	0			152					(152)
Acquisition of redeemable noncontrolling interest	0
Acquisition of noncontrolling interest	1,153								1,153
Net income attributable to redeemable noncontrolling interests	(176)			(176)
Change in redemption value of redeemable noncontrolling interests	32		32
Dividends paid on common stock	(29,553)			(29,553)
Repurchase of Class B common stock	(2,103)							(2,103)
Issuance of Class B common stock, net of restricted stock award forfeitures	239		(3,721)					3,960
Amortization of unearned stock compensation and stock option expense	6,521		6,521
Other comprehensive income (loss), net of income taxes	99,466					99,466
Purchase of redeemable noncontrolling interest	0
As of at Dec. 31, 2019	3,326,796		381,669	6,534,427		303,295		(3,920,152)	7,557	964	19,036
Increase (Decrease) in Temporary Equity [Roll Forward]
Acquisition of redeemable noncontrolling interest	1,715
Net income attributable to redeemable noncontrolling interests	176
Change in redemption value of redeemable noncontrolling interests	(32)
Purchase of redeemable noncontrolling interest	(550)
As of at Dec. 31, 2019	5,655
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the year	299,968			299,968
Net loss attributable to noncontrolling interest	0			386					(386)
Acquisition of redeemable noncontrolling interest	0
Net income attributable to redeemable noncontrolling interests	11			11
Change in redemption value of redeemable noncontrolling interests	273								273
Distribution to noncontrolling interest	(353)								(353)
Dividends paid on common stock	(29,970)			(29,970)
Repurchase of Class B common stock	(161,829)							(161,829)
Issuance of Class B common stock, net of restricted stock award forfeitures	24,577		(411)					24,988
Amortization of unearned stock compensation and stock option expense	6,901		6,901
Other comprehensive income (loss), net of income taxes	300,019					300,019
As of at Dec. 31, 2020	3,766,393		$ 388,159	$ 6,804,822		$ 603,314		$ (4,056,993)	$ 7,091	$ 964	$ 19,036
Increase (Decrease) in Temporary Equity [Roll Forward]
Acquisition of redeemable noncontrolling interest	6,005
Net income attributable to redeemable noncontrolling interests	(11)
Change in redemption value of redeemable noncontrolling interests	279
As of at Dec. 31, 2020	$ 11,928