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, 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	58,378					58,378
Other comprehensive income, net of tax	5,504						5,504
Cash dividends declared on common stock	(7,325)					(7,325)
Dividends on preferred stock	(3,628)					(3,628)
Stock-based compensation	2,918			2,918
Common stock issued for:
Exercise of stock options and warrants	12,784		512	12,272
Restricted stock awards	(295)		74	(74)	(295)
Employee stock purchase plan	624		9	615
Director compensation plan	406		32	374
Balance at the end at Mar. 31, 2017	2,764,983	251,257	52,605	1,381,886	(4,884)	1,143,943	(59,824)
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	81,981					81,981
Other comprehensive income, net of tax	(26,406)						(26,406)
Cash dividends declared on common stock	(10,663)					(10,663)
Dividends on preferred stock	(2,050)					(2,050)
Stock-based compensation	3,683			3,683
Common stock issued for:
Exercise of stock options and warrants	7,196		179	7,017
Restricted stock awards	(369)		90	(90)	(369)
Employee stock purchase plan	630		8	622
Director compensation plan	425		19	406
Balance at the end at Mar. 31, 2018	$ 3,031,250	$ 125,000	$ 56,364	$ 1,540,673	$ (5,355)	$ 1,387,663	$ (73,095)