Condensed Consolidated Statements of Changes in Common Stockholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]
As of at Dec. 31, 2017	$ 2,915,145	$ 20,000	$ 370,700	$ 5,791,724	$ 535,555	$ (3,802,834)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the period	42,965			42,965
Net income attributable to redeemable noncontrolling interests	(73)			(73)
Dividends on common stock	(14,638)			(14,638)
Repurchase of Class B Common Stock	(79,001)					(79,001)
Issuance of Class B common stock, net of restricted stock awards and forfeitures	(70)		(189)			119
Amortization of unearned stock compensation and stock option expense	2,325		2,325
Other comprehensive income, net of income taxes	10,812				10,812
As of at Mar. 31, 2018	2,884,388	20,000	372,836	6,021,790	351,478	(3,881,716)	0
As of at Dec. 31, 2017	4,607
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income attributable to redeemable noncontrolling interests	73
As of at Mar. 31, 2018	4,680
As of at Dec. 31, 2018	2,916,782	20,000	378,837	6,236,125	203,829	(3,922,009)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income for the period	81,702			81,702
Contribution of noncontrolling interest	6,000						6,000
Net loss attributable to noncontrolling interest	0			62			(62)
Net income attributable to redeemable noncontrolling interests	(16)			(16)
Change in redemption value of redeemable noncontrolling interest	(54)		(54)
Dividends on common stock	(14,779)			(14,779)
Issuance of Class B common stock, net of restricted stock awards and forfeitures	(28)		(3,783)			3,755
Amortization of unearned stock compensation and stock option expense	1,639		1,639
Other comprehensive income, net of income taxes	8,290				8,290
Purchase of redeemable noncontrolling interest	0
As of at Mar. 31, 2019	2,999,536	$ 20,000	$ 376,639	$ 6,303,094	$ 212,119	$ (3,918,254)	$ 5,938
As of at Dec. 31, 2018	4,346
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income attributable to redeemable noncontrolling interests	16
Change in redemption value of redeemable noncontrolling interests	54
Purchase of redeemable noncontrolling interest	(550)
As of at Mar. 31, 2019	$ 3,866