Consolidated Statements Of Changes In Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Accumulated other comprehensive loss	Series C Preferred Stock Preferred stock	Series C Preferred Stock Common stock	Series C Preferred Stock Surplus
Balance at the beginning at Dec. 31, 2016	$ 2,695,617	$ 251,257	$ 51,978	$ 1,365,781	$ (4,589)	$ 1,096,518	$ (65,328)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	123,275					123,275
Other comprehensive income, net of tax	18,791						18,791
Cash dividends declared on common stock	(15,118)					(15,118)
Dividends on preferred stock	(5,678)					(5,678)
Stock-based compensation	5,746			5,746
Conversion of Series C preferred stock to common stock								$ (126,257)	$ 3,121	$ 123,136
Common stock issued for:
Exercise of stock options and warrants	15,061		573	14,488
Restricted stock awards	(295)		79	(79)	(295)
Employee stock purchase plan	1,249		19	1,230
Director compensation plan	810		32	778
Balance at the end at Jun. 30, 2017	2,839,458	125,000	55,802	1,511,080	(4,884)	1,198,997	(46,537)
Balance at the beginning at Mar. 31, 2017							(59,824)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,897
Other comprehensive income, net of tax	13,287
Balance at the end at Jun. 30, 2017	2,839,458	125,000	55,802	1,511,080	(4,884)	1,198,997	(46,537)
Balance at the beginning at Dec. 31, 2017	2,976,939	125,000	56,068	1,529,035	(4,986)	1,313,657	(41,835)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	171,561					171,561
Other comprehensive income, net of tax	(34,527)						(34,527)
Cash dividends declared on common stock	(21,362)					(21,362)
Dividends on preferred stock	(4,100)					(4,100)
Stock-based compensation	7,098			7,098
Common stock issued for:
Exercise of stock options and warrants	9,659		243	9,416
Restricted stock awards	(369)		92	(92)	(369)
Employee stock purchase plan	1,238		15	1,223
Director compensation plan	850		19	831
Balance at the end at Jun. 30, 2018	3,106,871	125,000	56,437	1,547,511	(5,355)	1,464,494	(81,216)
Balance at the beginning at Mar. 31, 2018							(73,095)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	89,580
Other comprehensive income, net of tax	(8,121)
Balance at the end at Jun. 30, 2018	$ 3,106,871	$ 125,000	$ 56,437	$ 1,547,511	$ (5,355)	$ 1,464,494	$ (81,216)