Consolidated Statements of Changes in Common Shareholders' Equity - USD ($) $ in Thousands	Total	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Class A Common Stock [Member] Common Stock [Member]	Class B Common Stock [Member] Common Stock [Member]
As of at Dec. 31, 2016	$ 2,452,941	$ 364,363	$ 5,588,942	$ 236,486	$ (3,756,850)	$ 0	$ 964	$ 19,036
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the year	302,489		302,489
Acquisition of redeemable noncontrolling interest	0
Net income attributable to redeemable noncontrolling interests	(445)		(445)
Change in redemption value of redeemable noncontrolling interests	(446)	(446)
Dividends paid on common stock	(28,329)		(28,329)
Repurchase of Class B common stock	(50,770)				(50,770)
Issuance of Class B common stock, net of restricted stock award forfeitures	385	(4,401)			4,786
Amortization of unearned stock compensation and stock option expense	11,184	11,184
Other comprehensive income (loss), net of income taxes	228,136			228,136
Reclassification of stranded tax effects as a result of tax reform	0		(70,933)	70,933
As of at Dec. 31, 2017	2,915,145	370,700	5,791,724	535,555	(3,802,834)	0	964	19,036
As of at Dec. 31, 2016	50
Increase (Decrease) in Temporary Equity [Roll Forward]
Acquisition of redeemable noncontrolling interest	3,666
Net income attributable to redeemable noncontrolling interests	445
Change in redemption value of redeemable noncontrolling interests	446
As of at Dec. 31, 2017	4,607
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
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