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	161,907						161,907
Other comprehensive income, net of tax	(30,405)										(30,405)
Dividends and dividend equivalents declared on common stock	(54,179)					99	(54,278)
Dividends on preferred stock		$ (3,938)						$ (3,938)
Stockholders' Equity, Other			$ 22						$ 22
Stock-based compensation	5,879					(1,541)	1,654			5,766
Exercise of stock options	2,110					(5,308)				7,418
Common shares acquired from stock compensation plan activity	(8,092)									(8,092)
Common stock repurchase program	(12,158)									(12,158)
Stock Issued During Period, Value, Other			(19)
Ending Balance at Jun. 30, 2018	2,761,723			145,037	937	1,115,414	1,699,767			(77,496)	(121,936)
Beginning Balance at Mar. 31, 2018	2,716,142			145,037	937	1,120,522	1,649,524			(84,399)	(115,479)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	81,682						81,682
Other comprehensive income, net of tax	(6,457)										(6,457)
Dividends and dividend equivalents declared on common stock	(30,111)					56	(30,167)
Dividends on preferred stock		$ (1,969)						$ (1,969)
Stockholders' Equity, Other			0						0
Stock-based compensation	2,544						697			1,847
Exercise of stock options	1,820					(5,164)				6,984
Common shares acquired from stock compensation plan activity	(1,928)									(1,928)
Common stock repurchase program	0									0
Stock Issued During Period, Value, Other			0
Ending Balance at Jun. 30, 2018	2,761,723			145,037	937	1,115,414	1,699,767			(77,496)	(121,936)
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	198,385						198,385
Other comprehensive income, 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)
Stock-based compensation	6,416					1,528	1,179			3,709
Exercise of stock options	621					(2,029)				2,650
Common shares acquired from stock compensation plan activity	(6,245)									(6,245)
Common stock repurchase program	(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)
Beginning Balance at Mar. 31, 2019	2,966,255			145,037	937	1,113,107	1,895,870			(86,855)	(101,841)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	98,649						98,649
Other comprehensive income, 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)
Stock-based compensation	3,440					1,528	275			1,637
Exercise of stock options	217					(742)	0			959
Common shares acquired from stock compensation plan activity	(134)									(134)
Common stock repurchase program	0									0
Ending Balance at Jun. 30, 2019	3,065,217			$ 145,037	$ 937	$ 1,113,893	1,955,933			$ (84,393)	$ (66,190)
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (515)						$ (515)