Condensed Financial Information - Parent Company - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net earnings		$ 234,475	$ 227,562	$ 202,034
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization		12,762	13,061	12,793
Gain on sale of assets, net		(4,115)	(1,217)	(4,001)
Decrease (increase) in other assets		907	(11,308)	(23,233)
Increase (decrease) in other liabilities		(27,801)	12,697	24,122
Cash flows from investing activities:
Maturity of available-for-sale securities		4,132,928	8,495,614	6,075,017
Purchases of bank premises and equipment and software		(15,784)	(19,205)	(16,450)
Cash flows from financing activities:
Cash dividends paid		(91,315)	(79,712)	(70,318)
Repurchase of stock		(9,449)	0	(8,008)
Net increase in cash and cash equivalents		(197,910)	(200,496)	446,480
CASH AND CASH EQUIVALENTS, beginning of year		528,588	729,084	282,604
CASH AND CASH EQUIVALENTS, end of year		330,678	528,588	729,084
Parent Company [Member]
Cash flows from operating activities:
Net earnings		234,475	227,562	202,034
Adjustments to reconcile net earnings to net cash provided by operating activities:
Excess of earnings over dividends of subsidiaries (1)	[1]	(174,741)	(140,441)	(122,997)
Depreciation and amortization		188	189	198
Gain on sale of assets, net			0	(38)
Decrease (increase) in other assets		645	(693)	164
Increase (decrease) in other liabilities		933	2,997	2,083
Other			(4)	35
Net cash provided by operating activities		61,500	89,610	81,479
Cash flows from investing activities:
Maturity of available-for-sale securities			0	3,720
Purchases of bank premises and equipment and software		(385)	(106)
Net cash provided by (used in) investing activities		(385)	(106)	3,720
Cash flows from financing activities:
Proceeds from stock option exercises		6,545	5,905	4,717
Cash dividends paid		(91,315)	(79,712)	(70,318)
Repurchase of stock		(9,449)	0	(8,008)
Net cash used in financing activities		(94,219)	(73,807)	(73,609)
Net increase in cash and cash equivalents		(33,104)	15,697	11,590
CASH AND CASH EQUIVALENTS, beginning of year		152,363	136,666	125,076
CASH AND CASH EQUIVALENTS, end of year		$ 119,259	$ 152,363	$ 136,666

[1] Eliminates in consolidation