Condensed Financial Information - Parent Company - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net earnings		$ 227,562	$ 202,034	$ 164,812
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization		13,061	12,793	11,665
Gain on sale of assets, net		(1,217)	(4,001)	(1,477)
Decrease (increase) in other assets		(11,308)	(23,233)	1,851
Increase (decrease) in other liabilities		12,697	24,122	4,374
Cash flows from investing activities:
Maturity of available-for-sale securities		8,495,614	6,075,017	4,460,703
Purchases of bank premises and equipment and software		(19,205)	(16,450)	(8,671)
Cash flows from financing activities:
Cash dividends paid		(79,712)	(70,318)	(61,056)
Repurchase of stock			(8,008)
Net increase in cash and cash equivalents		(200,496)	446,480	33,957
CASH AND CASH EQUIVALENTS, beginning of year		729,084	282,604	248,647
CASH AND CASH EQUIVALENTS, end of year		528,588	729,084	282,604
Parent Company [Member]
Cash flows from operating activities:
Net earnings		227,562	202,034	164,812
Adjustments to reconcile net earnings to net cash provided by operating activities:
Excess of earnings over dividends of subsidiaries (1)	[1]	(140,441)	(122,997)	(86,956)
Depreciation and amortization		189	198	246
Gain on sale of assets, net		0	(38)
Decrease (increase) in other assets		(693)	164	1,508
Increase (decrease) in other liabilities		2,997	2,083	990
Other		(4)	35
Net cash provided by operating activities		89,610	81,479	80,600
Cash flows from investing activities:
Maturity of available-for-sale securities		0	3,720
Purchases of bank premises and equipment and software		(106)		(24)
Net cash provided by (used in) investing activities		(106)	3,720	(24)
Cash flows from financing activities:
Proceeds from stock option exercises		5,905	4,717	4,294
Cash dividends paid		(79,712)	(70,318)	(61,056)
Repurchase of stock		0	(8,008)
Net cash used in financing activities		(73,807)	(73,609)	(56,762)
Net increase in cash and cash equivalents		15,697	11,590	23,814
CASH AND CASH EQUIVALENTS, beginning of year		136,666	125,076	101,262
CASH AND CASH EQUIVALENTS, end of year		$ 152,363	$ 136,666	$ 125,076

[1] Eliminates in consolidation