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 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]
Cumulative effect adjustment from the adoption of ASU 2018-02	(2,974)					2,974	(2,974)
Balance 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 loss, net of tax	(34,527)						(34,527)
Cash dividends declared on common stock	(21,362)					(21,362)
Dividends on preferred stock, $0.82 per share	(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 Jun. 30, 2018	3,106,871	125,000	56,437	1,547,511	(5,355)	1,464,494	(81,216)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment from the adoption of new accounting pronouncement | ASU 2016-01	(1,880)					1,880	(1,880)
Cumulative effect adjustment from the adoption of new accounting pronouncement | ASU 2017-12	(116)					(116)
Balance at Mar. 31, 2018	3,031,250	125,000	56,364	1,540,673	(5,355)	1,387,663	(73,095)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	89,580					89,580
Other comprehensive loss, net of tax	(8,121)						(8,121)
Cash dividends declared on common stock	(10,699)					(10,699)
Dividends on preferred stock, $0.82 per share	(2,050)					(2,050)
Stock-based compensation	3,415			3,415
Common stock issued for:
Exercise of stock options and warrants	2,463		64	2,399
Restricted stock awards			2	(2)
Employee stock purchase plan	608		7	601
Director compensation plan	425			425
Balance at Jun. 30, 2018	3,106,871	125,000	56,437	1,547,511	(5,355)	1,464,494	(81,216)
Balance at Dec. 31, 2018	3,267,570	125,000	56,518	1,557,984	(5,634)	1,610,574	(76,872)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	170,612					170,612
Other comprehensive loss, net of tax	31,443						31,443
Cash dividends declared on common stock	(28,289)					(28,289)
Dividends on preferred stock, $0.82 per share	(4,100)					(4,100)
Stock-based compensation	6,283			6,283
Common stock issued for:
Exercise of stock options and warrants	3,027		95	3,507	(575)
Restricted stock awards	(441)		142	(142)	(441)
Employee stock purchase plan	1,349		21	1,328
Director compensation plan	1,027		18	1,009
Balance at Jun. 30, 2019	3,446,950	125,000	56,794	1,569,969	(6,650)	1,747,266	(45,429)
Balance at Mar. 31, 2019	3,371,972	125,000	56,765	1,565,185	(6,650)	1,682,016	(50,344)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	81,466					81,466
Other comprehensive loss, net of tax	4,915						4,915
Cash dividends declared on common stock	(14,166)					(14,166)
Dividends on preferred stock, $0.82 per share	(2,050)					(2,050)
Stock-based compensation	2,965			2,965
Common stock issued for:
Exercise of stock options and warrants	659		16	643
Restricted stock awards			3	(3)
Employee stock purchase plan	666		10	656
Director compensation plan	523			523
Balance at Jun. 30, 2019	$ 3,446,950	$ 125,000	$ 56,794	$ 1,569,969	$ (6,650)	$ 1,747,266	$ (45,429)