Securities

9 Months Ended

Sep. 30, 2025

Cash and Cash Equivalents [Abstract]

Note 2 - Securities

Debt securities have been classified in the consolidated balance sheets according to management’s intent. The amortized cost, related gross unrealized gains and losses, allowance for credit losses and the fair value of available-for-sale securities are as follows (dollars in thousands):


	September 30, 2025
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	102,865	$	2	$	(897	)	$	101,970
Obligations of states and political subdivisions		1,859,132		8,751		(133,972	)		1,733,911
Residential mortgage-backed securities		2,737,201		5,622		(272,025	)		2,470,798
Commercial mortgage-backed securities		849,026		8,580		(3,418	)		854,188
Corporate bonds and other		103,544		20		(3,618	)		99,946
Total securities available-for-sale	$	5,651,768	$	22,975	$	(413,930	)	$	5,260,813


	September 30, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	298,671	$	14	$	(5,671	)	$	293,014
Obligations of states and political subdivisions		1,586,300		699		(115,516	)		1,471,483
Residential mortgage-backed securities		2,712,305		1,655		(290,030	)		2,423,930
Commercial mortgage-backed securities		320,685		1,946		(5,795	)		316,836
Corporate bonds and other		112,163		59		(5,186	)		107,036
Total securities available-for-sale	$	5,030,124	$	4,373	$	(422,198	)	$	4,612,299


	December 31, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	278,155	$	2	$	(4,595	)	$	273,562
Obligations of states and political subdivisions		1,578,749		338		(138,842	)		1,440,245
Residential mortgage-backed securities		2,729,096		184		(378,746	)		2,350,534
Commercial mortgage-backed securities		457,311		99		(9,658	)		447,752
Corporate bonds and other		111,994		50		(6,378	)		105,666
Total securities available-for-sale	$	5,155,305	$	673	$	(538,219	)	$	4,617,759

The Company invests in mortgage-backed securities that have expected maturities that differ from their contractual maturities. These differences arise because borrowers may have the right to call or prepay obligations with or without a prepayment penalty. These securities include collateralized mortgage obligations (CMOs) and other asset backed securities. The expected maturities of these securities at September 30, 2025 and 2024, and December 31, 2024, were computed by using scheduled amortization of balances and historical prepayment rates.

The carrying value and estimated fair value of available-for-sale securities at September 30, 2025, by contractual and expected maturity, are shown below (dollars in thousands):


	Carrying		Estimated
	Value		Fair Value
Due within one year	$	225,746	$	223,945
Due after one year through five years		2,493,891		2,383,120
Due after five years through ten years		2,145,923		1,966,228
Due after ten years		786,208		687,520
Total	$	5,651,768	$	5,260,813

The following tables disclose as of September 30, 2025 and 2024, and December 31, 2024, the Company’s investment securities that have been in a continuous unrealized-loss position for less than 12 months and for 12 or more months (dollars in thousands):


	Less than 12 Months					12 Months or Longer					Total
September 30, 2025	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	1,000	$	—		$	99,476	$	(897	)	$	100,476	$	(897	)
Obligations of states and political subdivisions		21,278		(854	)		1,344,598		(133,118	)		1,365,876		(133,972	)
Residential mortgage-backed securities		125,497		(450	)		2,042,826		(271,575	)		2,168,323		(272,025	)
Commercial mortgage-backed securities		66,851		(74	)		166,330		(3,344	)		233,181		(3,418	)
Corporate bonds and other		—		—			82,982		(3,618	)		82,982		(3,618	)
Total	$	214,626	$	(1,378	)	$	3,736,212	$	(412,552	)	$	3,950,838	$	(413,930	)


	Less than 12 Months					12 Months or Longer					Total
September 30, 2024	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	—	$	—		$	290,535	$	(5,671	)	$	290,535	$	(5,671	)
Obligations of states and political subdivisions		6,899		(43	)		1,395,597		(115,473	)		1,402,496		(115,516	)
Residential mortgage-backed securities		124,439		(335	)		2,205,425		(289,695	)		2,329,864		(290,030	)
Commercial mortgage-backed securities		7,118		(32	)		209,632		(5,763	)		216,750		(5,795	)
Corporate bonds and other		—		—			97,183		(5,186	)		97,183		(5,186	)
Total	$	138,456	$	(410	)	$	4,198,372	$	(421,788	)	$	4,336,828	$	(422,198	)


	Less than 12 Months					12 Months or Longer					Total
December 31, 2024	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	—	$	—		$	271,088	$	(4,595	)	$	271,088	$	(4,595	)
Obligations of states and political subdivisions		56,777		(1,224	)		1,361,628		(137,618	)		1,418,405		(138,842	)
Residential mortgage-backed securities		198,385		(4,990	)		2,048,727		(373,756	)		2,247,112		(378,746	)
Commercial mortgage-backed securities		196,640		(2,249	)		190,189		(7,409	)		386,829		(9,658	)
Corporate bonds and other		4,871		(44	)		95,840		(6,334	)		100,711		(6,378	)
Total	$	456,673	$	(8,507	)	$	3,967,472	$	(529,712	)	$	4,424,145	$	(538,219	)

The number of investments in an unrealized loss position totaled 682 at September 30, 2025. We believe any unrealized losses in the U.S. treasury securities, obligations of state and political subdivisions, residential and commercial mortgage-backed and asset-backed investment securities, and corporate bonds and other at September 30, 2025 and 2024, and December 31, 2024, are due to changes in interest rates and not credit-related events. As such, no allowance for credit losses is required on these securities at September 30, 2025 and 2024, and December 31, 2024. Unrealized losses on investment securities are expected to recover over time as these securities approach maturity. Based on evaluations of impaired securities as of September 30, 2025, the Company does not intend to sell any impaired available-for-sale securities before fair value recovers to the current amortized cost, and it is more-likely-than-not that the Company will not be required to sell impaired securities before fair value recovers, which may be maturity. Our mortgage related securities are backed by GNMA, FNMA and FHLMC or are collateralized by securities backed by these agencies. At September 30, 2025, 72.57% of our available-for-sale securities that are obligations of states and political subdivisions were issued within the State of Texas, of which 55.25% are guaranteed by the Texas Permanent School Fund.

Securities, carried at approximately $2,335,928,000 on September 30, 2025, were pledged as collateral for public or trust fund deposits, repurchase agreements, borrowings and for other purposes required or permitted by law.

During the three and nine-months ended September 30, 2025 and 2024, respectively, there were no sales of investment securities that were classified as available-for-sale. There were no gross realized security gains or losses from sales during the three and nine-months ended September 30, 2025 and 2024.

The specific identification method was used to determine cost in order to compute the realized gains and losses.