Consolidated Statement of Shareholder Equity Statement - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Series E Preferred Stock [Member]	Series F Preferred Stock [Member]	Common Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Retained Earnings [Member] Series E Preferred Stock [Member]	Retained Earnings [Member] Series F Preferred Stock [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]
Beginning Balance at Dec. 31, 2017	$ 2,701,958					$ 145,056	$ 937	$ 1,122,164	$ 1,595,762				$ (70,430)	$ (91,531)
Beginning Balance (Accountign Standards Update 2017-08 and 2016-01) at Dec. 31, 2017		$ (1,373)								$ (1,373)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax														94,580
Ending Balance at Sep. 30, 2018														(36,072)
Beginning Balance at Dec. 31, 2017	2,701,958					145,056	937	1,122,164	1,595,762				(70,430)	(91,531)
Beginning Balance (Accountign Standards Update 2017-08 and 2016-01) at Dec. 31, 2017		(1,373)								(1,373)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	360,418								360,418
Other Comprehensive Income (Loss), Net of Tax	(39,121)													(39,121)
Dividends, Common Stock	(115,343)							99	(115,442)
Dividends, Preferred Stock			$ (7,875)								$ (7,875)
Stockholders' Equity, Other				$ (22)								$ 22
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	11,612							(1,541)	3,275				9,878
Stock Issued During Period, Value, Stock Options Exercised	2,173							(5,762)					7,935
Stock Issued During Period, Value, Conversion of Units	0							(566)	(6,484)				7,050
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(13,779)												(13,779)
Stock Repurchased During Period, Value	(12,158)												(12,158)
Stock Issued During Period, Value, Other	(19)					(19)
Ending Balance at Dec. 31, 2018	2,886,515	(513)				145,037	937	1,114,394	1,828,303	(513)			(71,504)	(130,652)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared					$ 1.25
Preferred Stock, Dividends Per Share, Declared			$ 1,323.44
Other Comprehensive Income (Loss), Net of Tax														78,328
Ending Balance at Sep. 30, 2019														42,256
Beginning Balance at Dec. 31, 2018	$ 2,886,515	(513)				145,037	937	1,114,394	1,828,303	(513)			(71,504)	(130,652)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Net income	$ 382,723								382,723
Other Comprehensive Income (Loss), Net of Tax	94,580													94,580
Dividends, Common Stock	(141,286)								(141,286)
Dividends, Preferred Stock				$ (7,875)								(7,875)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	12,626							885					11,741
Stock Issued During Period, Value, Stock Options Exercised	619							(2,029)					2,648
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(6,616)												(6,616)
Stock Repurchased During Period, Value	(13,003)												(13,003)
Ending Balance at Dec. 31, 2019	3,207,770	(51,213)				145,037	937	1,113,250	2,061,352	(51,213)			(76,734)	(36,072)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared					1.53
Preferred Stock, Dividends Per Share, Declared				$ 1,312.50
Beginning Balance at Sep. 30, 2019														42,256
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	90,473
Ending Balance at Dec. 31, 2019	$ 3,207,770	$ (51,213)				145,037	937	1,113,250	2,061,352	$ (51,213)			(76,734)	(36,072)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Net income	$ 220,621								220,621
Other Comprehensive Income (Loss), Net of Tax	78,328													78,328
Dividends, Common Stock	(145,363)								(145,363)
Dividends, Preferred Stock				$ (7,875)								$ (7,875)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	12,179							(3,524)					15,703
Stock Issued During Period, Value, Stock Options Exercised	240							(194)					434
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(3,506)												(3,506)
Stock Repurchased During Period, Value	(76,556)												(76,556)
Ending Balance at Dec. 31, 2020	$ 3,234,625					$ 145,037	$ 937	$ 1,109,532	$ 2,077,522				$ (140,659)	$ 42,256
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared					$ 1.60
Preferred Stock, Dividends Per Share, Declared				$ 1,312.50