Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2013	$ 2,514,161	$ 144,486	$ 617	$ 724,197	$ 1,575,282	$ 140,434	$ (70,855)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	277,977				277,977
Other comprehensive loss, net of tax	1,380					1,380
Proceeds from stock option exercises/stock unit conversions	29,158			(2,620)	(7,694)		39,472
Tax benefits from stock-based compensation	3,202			3,202
Stock-based compensation expense recognized in earnings	12,503			12,503
Non-vested stock awards and stock units	0			(506)			506
Common stock issued in acquisition of WNB Bancshares	149,720		20	149,700
Purchase of treasury stock	(1,457)						(1,457)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(127,178)				(127,178)
Balance at Dec. 31, 2014	2,851,403	144,486	637	886,476	1,710,324	141,814	(32,334)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	279,328				279,328
Other comprehensive loss, net of tax	(27,951)					(27,951)
Proceeds from stock option exercises/stock unit conversions	14,853			(2,248)	(4,240)		21,341
Tax benefits from stock-based compensation	1,434			1,434
Stock-based compensation expense recognized in earnings	12,737			12,737
Non-vested stock awards and stock units	0			(1,049)			1,049
Purchase of treasury stock	(101,237)						(101,237)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(132,161)				(132,161)
Balance at Dec. 31, 2015	2,890,343	144,486	637	897,350	1,845,188	113,863	(111,181)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	304,261				304,261
Other comprehensive loss, net of tax	(138,486)					(138,486)
Proceeds from stock option exercises/stock unit conversions	78,866			(2,417)	(20,915)		102,198
Stock-based compensation expense recognized in earnings	11,799			11,799
Purchase of treasury stock	(1,290)						(1,290)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(134,902)				(134,902)
Balance at Dec. 31, 2016	$ 3,002,528	$ 144,486	$ 637	$ 906,732	$ 1,985,569	$ (24,623)	$ (10,273)