Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 198,977,000	$ 234,475,000	$ 227,562,000
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	12,578,000	12,762,000	13,061,000
Provision for credit losses	10,631,000	17,427,000	(1,139,000)
Securities premium amortization, net	52,343,000	70,788,000	68,308,000
Discount accretion on purchased loans	0	(1,492,000)	(2,362,000)
Gain on sale of assets, net	5,548,000	(4,115,000)	(1,217,000)
Stock-based compensation	4,256,000	3,958,000	3,245,000
Net tax benefit from stock-based compensation	(319,000)	(336,000)	(428,000)
Deferred federal income tax (expense) benefit	(359,000)	(4,205,000)	3,531,000
Change in loans held-for-sale	(2,239,000)	25,194,000	44,098,000
Change in other assets	(3,895,000)	(1,281,000)	(11,317,000)
Change in other liabilities	6,663,000	(29,577,000)	10,953,000
Total adjustments	85,845,000	89,795,000	127,589,000
Net cash provided by operating activities	284,822,000	324,270,000	355,151,000
Activity in available-for-sale securities and other investments:
Sales	411,134,000	479,273,000	10,631,000
Maturities	4,443,813,000	4,132,928,000	8,495,614,000
Purchases	(4,005,743,000)	(4,385,683,000)	(10,887,727,000)
Net increase in loans held-for-investment	(708,432,000)	(1,049,925,000)	(211,786,000)
Purchases of bank premises and equipment	(17,251,000)	(15,784,000)	(19,205,000)
Proceeds from sale of bank premises and equipment and other assets	3,771,000	1,186,000	823,000
Net cash provided by (used in) investing activities	127,292,000	(838,005,000)	(2,611,650,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in noninterest-bearing deposits	(626,202,000)	281,558,000	797,533,000
Net increase in interest-bearing deposits	758,995,000	157,461,000	1,093,138,000
Net increase (decrease) in repurchase agreements and borrowings	(238,426,000)	(28,645,000)	241,059,000
Common stock transactions:
Proceeds from stock option exercises/stock unit conversions/restricted stock activity	2,133,000	6,215,000	3,985,000
Dividends paid	(99,965,000)	(91,315,000)	(79,712,000)
Repurchase of stock	(2,736,000)	(9,449,000)	0
Net cash provided by (used in) financing activities	(206,201,000)	315,825,000	2,056,003,000
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	205,913,000	(197,910,000)	(200,496,000)
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Beginning Balance	330,678,000	528,588,000	729,084,000
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Ending Balance	536,591,000	330,678,000	528,588,000
SUPPLEMENTAL INFORMATION AND NONCASH TRANSACTIONS:
Interest paid	135,167,000	30,540,000	6,198,000
Federal income taxes paid	46,677,000	45,430,000	39,528,000
Schedule of noncash investing and financing activities:
Assets acquired through foreclosure	$ 499,000	$ 0	$ 2,711,000