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, 2012	$ 2,417,482	$ 0	$ 615	$ 702,968	$ 1,475,851	$ 238,048	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,866				237,866
Other comprehensive loss, net of tax	(97,614)					(97,614)
Proceeds from stock option exercises	68,653		2	7,839	(12,097)		72,909
Tax benefits from stock-based compensation	2,293			2,293
Stock-based compensation expense recognized in earnings	11,963			11,963
Non-vested stock awards and stock units	0			(866)	0		866
Issuance of preferred stock	144,486	144,486
Purchase of treasury stock	(144,630)						(144,630)
Cash dividends paid on preferred stock	(6,719)				(6,719)
Cash dividends – common stock	(119,619)				(119,619)
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	29,158		0	(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)	0		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	14,853		0	(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)	0		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)