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	198,385									198,385
Other Comprehensive Income (Loss), Net of Tax	64,462														64,462
Dividends and dividend equivalents declared on common stock	(67,481)									(67,481)
Dividends on preferred stock			$ (3,938)									$ (3,938)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	6,416							1,528		1,179			3,709
Stock Issued During Period, Value, Stock Options Exercised	621							(2,029)					2,650
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(6,245)												(6,245)
Stock Repurchased During Period, Value	(13,003)												(13,003)
Ending Balance at Jun. 30, 2019	$ 3,065,217			145,037		937		1,113,893		1,955,933			(84,393)		(66,190)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.73
Dividends on preferred stock (in dollars per share)			$ 656.250
Beginning Balance at Mar. 31, 2019	$ 2,966,255	0		145,037	0	937	0	1,113,107	0	1,895,870	0		(86,855)	0	(101,841)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	98,649									98,649
Other Comprehensive Income (Loss), Net of Tax	35,651														35,651
Dividends and dividend equivalents declared on common stock	(36,892)									(36,892)
Dividends on preferred stock			$ (1,969)									(1,969)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	3,440							1,528		275			1,637
Stock Issued During Period, Value, Stock Options Exercised	217							(742)					959
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(134)												(134)
Stock Repurchased During Period, Value	0												0
Ending Balance at Jun. 30, 2019	$ 3,065,217			145,037		937		1,113,893		1,955,933			(84,393)		(66,190)
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	91,296									91,296
Other Comprehensive Income (Loss), Net of Tax	77,517														77,517
Dividends and dividend equivalents declared on common stock	(73,010)									(73,010)
Dividends on preferred stock			$ (3,938)									(3,938)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	6,014							(9,389)		0			15,403
Stock Issued During Period, Value, Stock Options Exercised	118							(105)					223
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(3,219)												(3,219)
Stock Repurchased During Period, Value	(76,556)												(76,556)
Ending Balance at Jun. 30, 2020	$ 3,174,779			145,037		937		1,103,756		2,024,487			(140,883)		41,445
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.80
Dividends on preferred stock (in dollars per share)			$ 656.250
Beginning Balance at Mar. 31, 2020	$ 3,090,242	$ 0		145,037	$ 0	937	$ 0	1,101,324	$ 0	2,009,541	$ 0		(141,797)	$ 0	(24,800)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,097									53,097
Other Comprehensive Income (Loss), Net of Tax	66,245														66,245
Dividends and dividend equivalents declared on common stock	(36,182)									(36,182)
Dividends on preferred stock			$ (1,969)									$ (1,969)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	3,405							2,432		0			973
Stock Issued During Period, Value, Stock Options Exercised	0							0					0
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(59)												(59)
Stock Repurchased During Period, Value	0												0
Ending Balance at Jun. 30, 2020	$ 3,174,779			$ 145,037		$ 937		$ 1,103,756		$ 2,024,487			$ (140,883)		$ 41,445
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