Securities

3 Months Ended

Mar. 31, 2025

Cash and Cash Equivalents [Abstract]

Securities

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):

	March 31, 2025
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	216,650	$	3	$	(2,979	)	$	213,674
Obligations of states and political subdivisions		1,569,885		239		(160,637	)		1,409,487
Residential mortgage-backed securities		2,727,421		2,126		(324,666	)		2,404,881
Commercial mortgage-backed securities		627,318		4,040		(5,697	)		625,661
Corporate bonds and other		111,825		64		(5,161	)		106,728
Total securities available-for-sale	$	5,253,099	$	6,472	$	(499,140	)	$	4,760,431

	March 31, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	445,399	$	—	$	(13,231	)	$	432,168
Obligations of states and political subdivisions		1,592,523		570		(139,058	)		1,454,035
Residential mortgage-backed securities		2,685,896		72		(386,691	)		2,299,277
Commercial mortgage-backed securities		381,198		52		(12,344	)		368,906
Corporate bonds and other		112,501		—		(8,361	)		104,140
Total securities available-for-sale	$	5,217,517	$	694	$	(559,685	)	$	4,658,526

	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 did not hold any securities classified as held-to-maturity at March 31, 2025, March 31, 2024, or December 31, 2024.

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 March 31, 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 March 31, 2025, by contractual and expected maturity, are shown below (dollars in thousands):

	Carrying		Estimated
	Value		Fair Value
Due within one year	$	279,646	$	276,226
Due after one year through five years		1,868,240		1,754,031
Due after five years through ten years		1,795,546		1,608,902
Due after ten years		1,309,667		1,121,272
Total	$	5,253,099	$	4,760,431

The following tables disclose as of March 31, 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
March 31, 2025	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	—	$	—		$	211,193	$	(2,979	)	$	211,193	$	(2,979	)
Obligations of states and political subdivisions		72,501		(2,111	)		1,329,121		(158,526	)		1,401,622		(160,637	)
Residential mortgage-backed securities		167,666		(1,950	)		2,059,869		(322,716	)		2,227,535		(324,666	)
Commercial mortgage-backed securities		16,992		(179	)		188,744		(5,518	)		205,736		(5,697	)
Corporate bonds and other		9,908		(14	)		91,832		(5,147	)		101,740		(5,161	)
Total	$	267,067	$	(4,254	)	$	3,880,759	$	(494,886	)	$	4,147,826	$	(499,140	)

	Less than 12 Months					12 Months or Longer					Total
March 31, 2024	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
U.S. Treasury securities	$	2,438	$	(16	)	$	429,730	$	(13,215	)	$	432,168	$	(13,231	)
Obligations of states and political subdivisions		33,073		(114	)		1,398,108		(138,944	)		1,431,181		(139,058	)
Residential mortgage-backed securities		22,586		(299	)		2,261,311		(386,392	)		2,283,897		(386,691	)
Commercial mortgage-backed securities		64,721		(507	)		275,924		(11,837	)		340,645		(12,344	)
Corporate bonds and other		—		—			104,140		(8,361	)		104,140		(8,361	)
Total	$	122,818	$	(936	)	$	4,469,213	$	(558,749	)	$	4,592,031	$	(559,685	)

	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 775 at March 31, 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 March 31, 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 March 31, 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 March 31, 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 March 31, 2025, 67.14% of our available-for-sale securities that are obligations of states and political subdivisions were issued within the State of Texas, of which 56.01% are guaranteed by the Texas Permanent School Fund.

Securities, carried at approximately $2,274,902,000 on March 31, 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-months ended March 31, 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 and calls during the first quarters of 2025 or 2024.

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