Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 223,511,000	$ 198,977,000	$ 234,475,000
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization, net	13,427,000	12,578,000	12,762,000
Provision for credit losses	13,821,000	10,631,000	17,427,000
Securities premium amortization, net	44,730,000	52,343,000	70,788,000
Discount accretion on purchased loans	0	0	(1,492,000)
(Gain) loss on sale of securities and other assets, net	(433,000)	5,548,000	(4,115,000)
Stock-based compensation	4,934,000	4,256,000	3,958,000
Net tax benefit from stock-based compensation	361,000	319,000	336,000
Deferred federal income tax (expense) benefit	(620,000)	(359,000)	(4,205,000)
Change in loans held-for-sale	5,855,000	(2,239,000)	25,194,000
Change in other assets	(7,122,000)	(3,895,000)	(1,281,000)
Change in other liabilities	11,177,000	6,663,000	(29,577,000)
Total adjustments	86,130,000	85,845,000	89,795,000
Net cash provided by operating activities	309,641,000	284,822,000	324,270,000
Activity in available-for-sale securities and other investments:
Sales	0	411,134,000	479,273,000
Maturities	6,643,108,000	4,443,813,000	4,132,928,000
Purchases	(6,599,462,000)	(4,005,743,000)	(4,385,683,000)
Net increase in loans held-for-investment	(765,702,000)	(708,432,000)	(1,049,925,000)
Purchases of bank premises and equipment	(16,720,000)	(17,251,000)	(15,784,000)
Proceeds from sale of bank premises and equipment and other assets	1,898,000	3,771,000	1,186,000
Net cash provided by (used in) investing activities	(736,878,000)	127,292,000	(838,005,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in noninterest-bearing deposits	(87,545,000)	(626,202,000)	281,558,000
Net increase in interest-bearing deposits	1,048,419,000	758,995,000	157,461,000
Net increase (decrease) in repurchase agreements and borrowings	(207,062,000)	(238,426,000)	(28,645,000)
Common stock transactions:
Proceeds from stock option exercises/stock unit conversions/restricted stock activity	3,160,000	2,133,000	6,215,000
Dividends paid	(102,913,000)	(99,965,000)	(91,315,000)
Repurchase of stock	0	(2,736,000)	(9,449,000)
Net cash provided by (used in) financing activities	654,059,000	(206,201,000)	315,825,000
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	226,822,000	205,913,000	(197,910,000)
CASH AND CASH EQUIVALENTS, beginning of year	536,591,000	330,678,000	528,588,000
CASH AND CASH EQUIVALENTS, end of year	763,413,000	536,591,000	330,678,000
SUPPLEMENTAL INFORMATION AND NONCASH TRANSACTIONS:
Interest paid	205,483,000	135,167,000	30,540,000
Federal income taxes paid	41,098,000	46,677,000	45,430,000
Schedule of noncash investing and financing activities:
Assets acquired through foreclosure	$ 1,899,000	$ 499,000	$ 0