CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Accumulated other comprehensive income (loss)
Beginning balance at Dec. 31, 2020	$ 4,115,995	$ 412,500	$ 58,473	$ 1,649,990	$ (100,363)	$ 2,080,013	$ 15,382
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	367,394					367,394
Other comprehensive loss, net of tax	(13,965)						(13,965)
Cash dividends declared on common stock	(52,987)					(52,987)
Dividends on preferred stock	(20,973)					(20,973)
Common stock repurchases under authorized program	(9,540)				(9,540)
Stock-based compensation	9,437			9,437
Common stock issued for:
Exercise of stock options and warrants	10,559		246	10,313
Restricted stock awards	0		13	(13)
Employee stock purchase plan	2,548		38	2,510
Director compensation plan	1,849		24	1,825
Ending balance at Sep. 30, 2021	4,410,317	412,500	58,794	1,674,062	(109,903)	2,373,447	1,417
Beginning balance at Jun. 30, 2021	4,339,011	412,500	58,770	1,669,002	(100,363)	2,288,969	10,133
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	109,137					109,137
Other comprehensive loss, net of tax	(8,716)						(8,716)
Cash dividends declared on common stock	(17,668)					(17,668)
Dividends on preferred stock	(6,991)					(6,991)
Common stock repurchases under authorized program	(9,540)				(9,540)
Stock-based compensation	3,243			3,243
Common stock issued for:
Exercise of stock options and warrants	318		8	310
Restricted stock awards	0		3	(3)
Employee stock purchase plan	928		13	915
Director compensation plan	595			595
Ending balance at Sep. 30, 2021	4,410,317	412,500	58,794	1,674,062	(109,903)	2,373,447	1,417
Beginning balance at Dec. 31, 2021	4,498,688	412,500	58,892	1,685,572	(109,903)	2,447,535	4,092
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	364,865					364,865
Other comprehensive loss, net of tax	(462,820)						(462,820)
Cash dividends declared on common stock	(59,583)					(59,583)
Dividends on preferred stock	(20,973)					(20,973)
Stock-based compensation	23,852			23,852
Common stock issued for:
New issuance, net of cost	285,721		1,612	174,206	109,903
Exercise of stock options and warrants	3,738		88	3,650
Restricted stock awards	0		61	(61)
Employee stock purchase plan	2,529		31	2,498
Director compensation plan	1,963		59	1,904
Ending balance at Sep. 30, 2022	4,637,980	412,500	60,743	1,891,621	0	2,731,844	(458,728)
Beginning balance at Jun. 30, 2022	4,727,623	412,500	60,722	1,880,913	0	2,616,525	(243,037)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	142,961					142,961
Other comprehensive loss, net of tax	(215,691)						(215,691)
Cash dividends declared on common stock	(20,651)					(20,651)
Dividends on preferred stock	(6,991)					(6,991)
Stock-based compensation	8,963			8,963
Common stock issued for:
Exercise of stock options and warrants	198		4	194
Restricted stock awards	0		5	(5)
Employee stock purchase plan	894		12	882
Director compensation plan	674		0	674
Ending balance at Sep. 30, 2022	$ 4,637,980	$ 412,500	$ 60,743	$ 1,891,621	$ 0	$ 2,731,844	$ (458,728)