Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Deferred Compensation [Member]	Accumulated Other Comprehensive Earnings (Loss) [Member]
Beginning Balance at Dec. 31, 2020	$ 1,678,190	$ 1,422	$ 669,644	$ 836,729	$ (9,126)	$ 9,126	$ 170,395
Beginning Balance, Shares at Dec. 31, 2020		142,161,834
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2020					(938,591)
Net earnings (Unaudited)	113,297			113,297
Stock option exercises (unaudited)	2,618	$ 2	2,616
Stock option exercises, Shares		165,371
Restricted stock grant/forfeiture, net (unaudited)	(663)		(663)
Restricted stock grant/forfeiture, net (unaudited), Shares		32,569
Cash dividends declared	(39,855)			(39,855)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(33,909)						(33,909)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (515)	515
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					(38)
Stock option expense (unaudited)	691		691
Ending Balance at Jun. 30, 2021	$ 1,720,369	$ 1,424	672,288	910,171	$ (9,641)	9,641	136,486
Ending Balance, Shares at Jun. 30, 2021		142,359,774
Treasury Stock, Ending Balance, Shares at Jun. 30, 2021	(938,629)				(938,629)
Beginning Balance at Mar. 31, 2021	$ 1,665,428	$ 1,423	671,849	875,147	$ (9,385)	9,385	117,009
Beginning Balance, Shares at Mar. 31, 2021		142,285,611
Treasury Stock, Beginning Balance, Shares at Mar. 31, 2021					(938,004)
Net earnings (Unaudited)	56,379			56,379
Stock option exercises (unaudited)	714	$ 1	713
Stock option exercises, Shares		40,847
Restricted stock grant/forfeiture, net (unaudited)	(646)		(646)
Restricted stock grant/forfeiture, net (unaudited), Shares		33,316
Cash dividends declared	(21,355)			(21,355)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	19,477						19,477
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (256)	256
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					(625)
Stock option expense (unaudited)	372		372
Ending Balance at Jun. 30, 2021	$ 1,720,369	$ 1,424	672,288	910,171	$ (9,641)	9,641	136,486
Ending Balance, Shares at Jun. 30, 2021		142,359,774
Treasury Stock, Ending Balance, Shares at Jun. 30, 2021	(938,629)				(938,629)
Beginning Balance at Dec. 31, 2021	$ 1,759,224	$ 1,425	676,871	981,675	$ (10,090)	10,090	99,253
Beginning Balance, Shares at Dec. 31, 2021		142,532,116
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2021	(936,897)				(936,897)
Net earnings (Unaudited)	$ 116,466			116,466
Stock option exercises (unaudited)	4,346	$ 3	4,343
Stock option exercises, Shares		234,585
Restricted stock grant/forfeiture, net (unaudited)	1,210		1,210
Restricted stock grant/forfeiture, net (unaudited), Shares		11,887
Cash dividends declared	(45,688)			(45,688)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(499,767)						(499,767)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (566)	566
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					(1,027)
Stock option expense (unaudited)	632		632
Shares repurchased under stock repurchase authorization (unaudited)	(7,405)	$ (2)	(7,403)
Shares repurchased under stock repurchase authorization (unaudited), Shares		(191,987)
Ending Balance at Jun. 30, 2022	$ 1,329,018	$ 1,426	675,653	1,052,453	$ (10,656)	10,656	(400,514)
Ending Balance, Shares at Jun. 30, 2022		142,586,601
Treasury Stock, Ending Balance, Shares at Jun. 30, 2022	(937,924)				(937,924)
Beginning Balance at Mar. 31, 2022	$ 1,488,749	$ 1,427	680,665	1,016,239	$ (10,404)	10,404	(209,582)
Beginning Balance, Shares at Mar. 31, 2022		142,704,495
Treasury Stock, Beginning Balance, Shares at Mar. 31, 2022					(936,847)
Net earnings (Unaudited)	60,494			60,494
Stock option exercises (unaudited)	1,425	$ 1	1,424
Stock option exercises, Shares		61,834
Restricted stock grant/forfeiture, net (unaudited)	651		651
Restricted stock grant/forfeiture, net (unaudited), Shares		12,259
Cash dividends declared	(24,280)			(24,280)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(190,932)						(190,932)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (252)	252
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					(1,077)
Stock option expense (unaudited)	316		316
Shares repurchased under stock repurchase authorization (unaudited)	(7,405)	$ (2)	(7,403)
Shares repurchased under stock repurchase authorization (unaudited), Shares		(191,987)
Ending Balance at Jun. 30, 2022	$ 1,329,018	$ 1,426	$ 675,653	$ 1,052,453	$ (10,656)	$ 10,656	$ (400,514)
Ending Balance, Shares at Jun. 30, 2022		142,586,601
Treasury Stock, Ending Balance, Shares at Jun. 30, 2022	(937,924)				(937,924)