Consolidated Statement of Changes in Shareholders' Equity (USD $)	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, 2011	$ 2,283,537,000	$ 0	$ 613,000	$ 680,803,000	$ 1,354,759,000	$ 247,734,000	$ (372,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,952,000				237,952,000
Other comprehensive income, net of tax	(9,686,000)					(9,686,000)
Stock option exercises/deferred stock unit conversions	10,516,000		2,000	10,100,000	(6,000)		420,000
Tax benefits from stock-based compensation	(384,000)			(384,000)
Stock-based compensation expense recognized in earnings	12,836,000			12,836,000
Non-vested stock awards and stock units	0			(387,000)	(1,000)		388,000
Purchase of treasury stock	(436,000)						(436,000)
Cash dividends – common stock	(116,853,000)				(116,853,000)
Balance at Dec. 31, 2012	2,417,482,000	0	615,000	702,968,000	1,475,851,000	238,048,000	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,866,000				237,866,000
Other comprehensive income, net of tax	(97,614,000)					(97,614,000)
Stock option exercises/deferred stock unit conversions	68,653,000		2,000	7,839,000	(12,097,000)		72,909,000
Tax benefits from stock-based compensation	2,293,000			2,293,000
Stock-based compensation expense recognized in earnings	11,963,000			11,963,000
Non-vested stock awards and stock units	0			(866,000)	0		866,000
Issuance of preferred stock	144,486,000	144,486,000
Purchase of treasury stock	(144,630,000)						(144,630,000)
Cash dividends – preferred stock	(6,719,000)				(6,719,000)
Cash dividends – common stock	(119,619,000)				(119,619,000)
Balance at Dec. 31, 2013	2,514,161,000	144,486,000	617,000	724,197,000	1,575,282,000	140,434,000	(70,855,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	277,977,000				277,977,000
Other comprehensive income, net of tax	1,380,000					1,380,000
Stock option exercises/deferred stock unit conversions	29,158,000			(2,620,000)	(7,694,000)		39,472,000
Tax benefits from stock-based compensation	3,202,000			3,202,000
Stock-based compensation expense recognized in earnings	12,503,000			12,503,000
Non-vested stock awards and stock units	0			(506,000)			506,000
Common stock issued in acquisition of WNB Bancshares	149,720,000		20,000	149,700,000
Purchase of treasury stock	(1,457,000)						(1,457,000)
Cash dividends – preferred stock	(8,063,000)				(8,063,000)
Cash dividends – common stock	(127,178,000)				(127,178,000)
Balance at Dec. 31, 2014	$ 2,851,403,000	$ 144,486,000	$ 637,000	$ 886,476,000	$ 1,710,324,000	$ 141,814,000	$ (32,334,000)