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)	172,225			172,225
Stock option exercises (unaudited)	4,676	$ 3	4,673
Stock option exercises, Shares		273,167
Restricted stock grant/forfeiture, net (unaudited)	(165)		(165)
Restricted stock grant/forfeiture, net (unaudited), Shares		32,686
Cash dividends declared	(61,230)			(61,230)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(60,948)						(60,948)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (750)	750
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					788
Stock option expense (unaudited)	987		987
Ending Balance at Sep. 30, 2021	$ 1,733,735	$ 1,425	675,139	947,724	$ (9,876)	9,876	109,447
Ending Balance, Shares at Sep. 30, 2021		142,467,687
Treasury Stock, Ending Balance, Shares at Sep. 30, 2021	(937,803)				(937,803)
Beginning Balance at Jun. 30, 2021	$ 1,720,369	$ 1,424	672,288	910,171	$ (9,641)	9,641	136,486
Beginning Balance, Shares at Jun. 30, 2021		142,359,774
Treasury Stock, Beginning Balance, Shares at Jun. 30, 2021					(938,629)
Net earnings (Unaudited)	58,928			58,928
Stock option exercises (unaudited)	2,058	$ 1	2,057
Stock option exercises, Shares		107,796
Restricted stock grant/forfeiture, net (unaudited)	498		498
Restricted stock grant/forfeiture, net (unaudited), Shares		117
Cash dividends declared	(21,375)			(21,375)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(27,039)						(27,039)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (235)	235
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					826
Stock option expense (unaudited)	296		296
Ending Balance at Sep. 30, 2021	$ 1,733,735	$ 1,425	675,139	947,724	$ (9,876)	9,876	109,447
Ending Balance, Shares at Sep. 30, 2021		142,467,687
Treasury Stock, Ending Balance, Shares at Sep. 30, 2021	(937,803)				(937,803)
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)	$ 175,807			175,807
Stock option exercises (unaudited)	5,974	$ 3	5,971
Stock option exercises, Shares		322,324
Restricted stock grant/forfeiture, net (unaudited)	1,681		1,681
Restricted stock grant/forfeiture, net (unaudited), Shares		18,282
Cash dividends declared	(69,939)			(69,939)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(731,674)						(731,674)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (817)	817
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					(3,745)
Stock option expense (unaudited)	991		991
Shares repurchased under stock repurchase authorization (unaudited)	(9,449)	$ (2)	(9,447)
Shares repurchased under stock repurchase authorization (unaudited), Shares		(244,559)
Ending Balance at Sep. 30, 2022	$ 1,132,615	$ 1,426	676,067	1,087,543	$ (10,907)	10,907	(632,421)
Ending Balance, Shares at Sep. 30, 2022		142,628,163
Treasury Stock, Ending Balance, Shares at Sep. 30, 2022	(933,152)				(933,152)
Beginning Balance at Jun. 30, 2022	$ 1,329,018	$ 1,426	675,653	1,052,453	$ (10,656)	10,656	(400,514)
Beginning Balance, Shares at Jun. 30, 2022		142,586,601
Treasury Stock, Beginning Balance, Shares at Jun. 30, 2022					(937,924)
Net earnings (Unaudited)	59,341			59,341
Stock option exercises (unaudited)	1,628		1,628
Stock option exercises, Shares		87,739
Restricted stock grant/forfeiture, net (unaudited)	471		471
Restricted stock grant/forfeiture, net (unaudited), Shares		(6,395)
Cash dividends declared	(24,251)			(24,251)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(231,907)						(231,907)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (251)	251
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					4,772
Stock option expense (unaudited)	359		359
Shares repurchased under stock repurchase authorization (unaudited)	(2,044)		(2,044)
Shares repurchased under stock repurchase authorization (unaudited), Shares		(52,572)
Ending Balance at Sep. 30, 2022	$ 1,132,615	$ 1,426	$ 676,067	$ 1,087,543	$ (10,907)	$ 10,907	$ (632,421)
Ending Balance, Shares at Sep. 30, 2022		142,628,163
Treasury Stock, Ending Balance, Shares at Sep. 30, 2022	(933,152)				(933,152)