Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Series E Preferred Stock [Member]	Series F Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series E Preferred Stock [Member]	Retained Earnings [Member] Series F Preferred Stock [Member]	Treasury Stock, at cost [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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	261,580						261,580
Other comprehensive income, net of tax	(40,033)										(40,033)
Dividends and dividend equivalents declared on common stock	(84,903)					99	(85,002)
Dividends on preferred stock		$ (5,906)						$ (5,906)
Stockholders' Equity, Other			$ 22						$ 22
Stock-based compensation	8,598					(1,541)	2,426			7,713
Exercise of stock options	2,110					(5,308)				7,418
Stock Issued During Period, Value, Conversion of Units	0					(566)	(6,484)			7,050
Common shares acquired from stock compensation plan activity	(13,689)									(13,689)
Common stock repurchase program	(12,158)									(12,158)
Stock Issued During Period, Value, Other	(19)		(19)
Ending Balance at Sep. 30, 2018	2,816,198			145,037	937	1,114,848	1,761,036			(74,096)	(131,564)
Beginning Balance at Jun. 30, 2018	2,761,723			145,037	937	1,115,414	1,699,767			(77,496)	(121,936)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	99,673						99,673
Other comprehensive income, net of tax	(9,628)										(9,628)
Dividends and dividend equivalents declared on common stock	(30,724)					0	(30,724)
Dividends on preferred stock		$ (1,968)						$ (1,968)
Stock-based compensation	2,719					0	772			1,947
Stock Issued During Period, Value, Conversion of Units	0					(566)	(6,484)			7,050
Common shares acquired from stock compensation plan activity	(5,597)									(5,597)
Ending Balance at Sep. 30, 2018	2,816,198			145,037	937	1,114,848	1,761,036			(74,096)	(131,564)
Cumulative Effect of New Accounting Principle in Period of Adoption	(1,362)						(1,362)
Beginning Balance at Dec. 31, 2018	2,886,515			145,037	937	1,114,394	1,828,303			(71,504)	(130,652)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	292,250						292,250
Other comprehensive income, 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)
Stock-based compensation	9,684					2,839	1,179			5,666
Exercise of stock options	621					(2,029)				2,650
Common shares acquired from stock compensation plan activity	(6,289)									(6,289)
Common stock repurchase program	(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)
Beginning 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]
Net income	93,865						93,865
Other comprehensive income, 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)
Stock-based compensation	3,268					1,311	0			1,957
Common shares acquired from stock compensation plan activity	(44)									(44)
Ending Balance at Sep. 30, 2019	3,152,394			$ 145,037	$ 937	$ 1,115,204	2,010,930			$ (82,480)	$ (37,234)
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (515)						$ (515)