Consolidated Statements of Shareholders' Equity (Unaudited) - 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, 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)
Net earnings (Unaudited)	175,807			175,807
Stock option exercises (unaudited)	5,974	$ 3	5,971
Stock option exercises, Shares		340,606
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)	2,672		2,672
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		94,134
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		830
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)
Beginning Balance at Dec. 31, 2022	$ 1,265,737	$ 1,427	677,593	1,121,945	$ (11,035)	11,035	(535,228)
Beginning Balance, Shares at Dec. 31, 2022		142,657,871
Treasury Stock, Beginning Balance, Shares at Dec. 31, 2022	(929,210)				(929,210)
Net earnings (Unaudited)	$ 152,997			152,997
Stock option exercises (unaudited)	1,483	$ 1	1,482
Stock option exercises, Shares		120,535
Cash dividends declared	(75,699)			(75,699)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(104,706)						(104,706)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)	623				$ (623)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					2,487
Stock option expense (unaudited)	3,033		3,033
Shares repurchased under stock repurchase authorization (unaudited)	$ (2,735)	$ (1)	(2,734)
Shares repurchased under stock repurchase authorization (unaudited), Shares	101,337	(101,337)
Ending Balance at Sep. 30, 2023	$ 1,240,110	$ 1,427	679,374	1,199,243	$ (11,658)	11,658	(639,934)
Ending Balance, Shares at Sep. 30, 2023		142,677,069
Treasury Stock, Ending Balance, Shares at Sep. 30, 2023	(926,723)				(926,723)
Beginning Balance at Jun. 30, 2023	$ 1,367,233	$ 1,427	680,676	1,175,410	$ (11,466)	11,466	(490,280)
Beginning Balance, Shares at Jun. 30, 2023		142,741,196
Treasury Stock, Beginning Balance, Shares at Jun. 30, 2023					(927,608)
Net earnings (Unaudited)	49,556			49,556
Stock option exercises (unaudited)	384	$ 1	383
Stock option exercises, Shares		37,210
Cash dividends declared	(25,723)			(25,723)
Change in unrealized gain (loss) in investment securities available-for-sale, net of related income taxes (unaudited)	(149,654)						(149,654)
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)					$ (192)	192
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), Shares					885
Stock option expense (unaudited)	1,049		1,049
Shares repurchased under stock repurchase authorization (unaudited)	(2,735)	$ (1)	(2,734)
Shares repurchased under stock repurchase authorization (unaudited), Shares		(101,337)
Ending Balance at Sep. 30, 2023	$ 1,240,110	$ 1,427	$ 679,374	$ 1,199,243	$ (11,658)	$ 11,658	$ (639,934)
Ending Balance, Shares at Sep. 30, 2023		142,677,069
Treasury Stock, Ending Balance, Shares at Sep. 30, 2023	(926,723)				(926,723)