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
Balance at the beginning at Dec. 31, 2015	$ 2,352,274	$ 251,287	$ 48,469	$ 1,190,988	$ (3,973)	$ 928,211	$ (62,708)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	152,267					152,267
Other comprehensive income, net of tax	30,129						30,129
Cash dividends declared on common stock	(17,846)					(17,846)
Dividends on preferred stock	(10,884)					(10,884)
Stock-based compensation	6,778			6,778
Conversion of Series C preferred stock to common stock	0	(30)	1	29
Common stock issued for:
New issuance, net of costs	152,823		3,000	149,823
Exercise of stock options and warrants	5,773		185	5,965	(377)
Restricted stock awards	37		88	121	(172)
Employee stock purchase plan	1,933		43	1,890
Director compensation plan	1,190		25	1,165
Balance at the end at Sep. 30, 2016	2,674,474	251,257	51,811	1,356,759	(4,522)	1,051,748	(32,579)
Balance at the beginning at Jun. 30, 2016							(34,440)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,115
Other comprehensive income, net of tax	1,861
Balance at the end at Sep. 30, 2016	2,674,474	251,257	51,811	1,356,759	(4,522)	1,051,748	(32,579)
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	188,901					188,901
Other comprehensive income, net of tax	23,842						23,842
Cash dividends declared on common stock	(22,932)					(22,932)
Dividends on preferred stock	(7,728)					(7,728)
Stock-based compensation	8,160			8,160
Conversion of Series C preferred stock to common stock	0	(126,257)	3,121	123,136
Common stock issued for:
Exercise of stock options and warrants	20,246		702	19,544
Restricted stock awards	(295)		79	(79)	(295)
Employee stock purchase plan	1,921		28	1,893
Director compensation plan	1,193		32	1,161
Balance at the end at Sep. 30, 2017	2,908,925	125,000	55,940	1,519,596	(4,884)	1,254,759	(41,486)
Balance at the beginning at Jun. 30, 2017							(46,537)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	65,626
Other comprehensive income, net of tax	5,051
Balance at the end at Sep. 30, 2017	$ 2,908,925	$ 125,000	$ 55,940	$ 1,519,596	$ (4,884)	$ 1,254,759	$ (41,486)