Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Series F Preferred Stock [Member]	Preferred Stock	Preferred Stock Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Common Stock Cumulative Effect, Period of Adoption, Adjustment	Paid-In Capital	Paid-In Capital Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings Series F Preferred Stock [Member]	Treasury Stock, at cost	Treasury Stock, at cost Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income, Net of Tax	Accumulated Other Comprehensive Income, Net of Tax Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance at Dec. 31, 2018	$ 2,886,515	$ (515)		$ 145,037	$ 0	$ 937	$ 0	$ 1,114,394	$ 0	$ 1,828,303	$ (515)		$ (71,504)	$ 0	$ (130,652)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	292,250									292,250
Other Comprehensive Income (Loss), Net of Tax	93,418														93,418
Dividends and dividend equivalents declared on common stock	(104,381)									(104,381)
Dividends on preferred stock			$ (5,906)									$ (5,906)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	9,684							2,839		1,179			5,666
Stock Issued During Period, Value, Stock Options Exercised	621							(2,029)					2,650
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(6,289)												(6,289)
Stock Repurchased During Period, Value	(13,003)												(13,003)
Ending Balance at Sep. 30, 2019	$ 3,152,394			145,037		937		1,115,204		2,010,930			(82,480)		(37,234)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 1.13
Dividends on preferred stock (in dollars per share)			$ 984.375
Beginning Balance at Jun. 30, 2019	$ 3,065,217	0		145,037	0	937	0	1,113,893	0	1,955,933	0		(84,393)	0	(66,190)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	93,865									93,865
Other Comprehensive Income (Loss), Net of Tax	28,956														28,956
Dividends and dividend equivalents declared on common stock	(36,900)									(36,900)
Dividends on preferred stock			$ (1,968)									(1,968)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	3,268							1,311		0			1,957
Stock Issued During Period, Value, Stock Options Exercised	0							0					0
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(44)												(44)
Stock Repurchased During Period, Value	0												0
Ending Balance at Sep. 30, 2019	$ 3,152,394			145,037		937		1,115,204		2,010,930			(82,480)		(37,234)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.40
Dividends on preferred stock (in dollars per share)			$ 328.125
Beginning Balance at Dec. 31, 2019	$ 3,207,770	(51,213)		145,037	0	937	0	1,113,250	0	2,061,352	(51,213)		(76,734)	0	(36,072)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	160,577									160,577
Other Comprehensive Income (Loss), Net of Tax	88,109														88,109
Dividends and dividend equivalents declared on common stock	(109,190)									(109,190)
Dividends on preferred stock			$ (5,906)									(5,906)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	9,356							(6,672)		0			16,028
Stock Issued During Period, Value, Stock Options Exercised	118							(105)					223
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(3,375)												(3,375)
Stock Repurchased During Period, Value	(76,556)												(76,556)
Ending Balance at Sep. 30, 2020	$ 3,219,690			145,037		937		1,106,473		2,055,620			(140,414)		52,037
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 1.20
Dividends on preferred stock (in dollars per share)			$ 984.375
Beginning Balance at Jun. 30, 2020	$ 3,174,779	$ 0		145,037	$ 0	937	$ 0	1,103,756	$ 0	2,024,487	$ 0		(140,883)	$ 0	41,445	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	69,281									69,281
Other Comprehensive Income (Loss), Net of Tax	10,592														10,592
Dividends and dividend equivalents declared on common stock	(36,180)									(36,180)
Dividends on preferred stock			$ (1,968)									$ (1,968)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	3,342							2,717		0			625
Stock Issued During Period, Value, Stock Options Exercised	0							0					0
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(156)												(156)
Stock Repurchased During Period, Value	0												0
Ending Balance at Sep. 30, 2020	$ 3,219,690			$ 145,037		$ 937		$ 1,106,473		$ 2,055,620			$ (140,414)		$ 52,037
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.40
Dividends on preferred stock (in dollars per share)			$ 328.125