Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Series E Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series E Preferred Stock [Member]	Treasury Stock, at cost [Member]	AOCI Attributable to Parent [Member]
Beginning Balance at Dec. 31, 2015	$ 2,413,960		$ 122,710	$ 937	$ 1,124,325	$ 1,315,948		$ (71,854)	$ (78,106)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	149,467					149,467
Other comprehensive income, net of tax	24,953								24,953
Dividends and dividend equivalents declared on common stock $0.25 and $0.23 per share during the 3 months ended March 31, 2017 and 2016, respectively	(66,979)				109	(67,088)
Dividends on Series E preferred stock $400.00 per share for the 3 months ended March 31, 2017 and 2016		$ (6,072)					$ (6,072)
Stock-based compensation, net of tax impact	10,689				2,413	245		8,031
Exercise of stock options	2,372				(1,307)			3,679
Common shares acquired related to stock compensation plan activity	(5,392)							(5,392)
Common stock repurchase program	(11,206)							(11,206)
Common stock warrants repurchased	(163)				(163)
Ending Balance at Sep. 30, 2016	2,511,629		122,710	937	1,125,377	1,392,500		(76,742)	(53,153)
Beginning Balance at Jun. 30, 2016									(57,511)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	51,817
Other comprehensive income, net of tax	4,358								4,358
Ending Balance at Sep. 30, 2016	2,511,629		122,710	937	1,125,377	1,392,500		(76,742)	(53,153)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Fair Value	4,125,125
Beginning Balance at Dec. 31, 2016	2,527,012		122,710	937	1,125,937	1,425,320		(70,899)	(76,993)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	185,546					185,546
Other comprehensive income, net of tax	7,895								7,895
Dividends and dividend equivalents declared on common stock $0.25 and $0.23 per share during the 3 months ended March 31, 2017 and 2016, respectively	(70,972)				124	(71,096)
Dividends on Series E preferred stock $400.00 per share for the 3 months ended March 31, 2017 and 2016		$ (6,072)					$ (6,072)
Stock-based compensation, net of tax impact	10,957					1,887		9,070
Exercise of stock options	5,301				(2,376)			7,677
Common shares acquired related to stock compensation plan activity	(9,295)							(9,295)
Common stock repurchase program	(11,585)							(11,585)
Ending Balance at Sep. 30, 2017	2,638,787		122,710	937	1,123,685	1,535,585		(75,032)	(69,098)
Beginning Balance at Jun. 30, 2017									(72,082)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,496
Other comprehensive income, net of tax	2,984								2,984
Ending Balance at Sep. 30, 2017	2,638,787		$ 122,710	$ 937	$ 1,123,685	$ 1,535,585		$ (75,032)	$ (69,098)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Fair Value	$ 4,481,675