Securities

6 Months Ended

Jun. 30, 2024

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):


	June 30, 2024
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	352,682	$	—	$	(10,706	)	$	341,976
Obligations of states and political subdivisions		1,584,389		420		(139,436	)		1,445,373
Residential mortgage-backed securities		2,705,508		71		(389,494	)		2,316,085
Commercial mortgage-backed securities		362,004		—		(11,982	)		350,022
Corporate bonds and other		127,868		—		(8,300	)		119,568
Total securities available-for-sale	$	5,132,451	$	491	$	(559,918	)	$	4,573,024


	June 30, 2023
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	508,124	$	—	$	(24,348	)	$	483,776
Obligations of states and political subdivisions		1,859,193		405		(166,634	)		1,692,964
Residential mortgage-backed securities		2,875,699		2		(402,760	)		2,472,941
Commercial mortgage-backed securities		331,829		—		(17,442	)		314,387
Corporate bonds and other		112,507		—		(10,313	)		102,194
Total securities available-for-sale	$	5,687,352	$	407	$	(621,497	)	$	5,066,262


	December 31, 2023
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	496,975	$	4	$	(14,745	)	$	482,234
Obligations of states and political subdivisions		1,621,405		934		(125,182	)		1,497,157
Residential mortgage-backed securities		2,716,968		7		(352,883	)		2,364,092
Commercial mortgage-backed securities		295,663		—		(11,339	)		284,324
Corporate bonds and other		112,670		—		(7,715	)		104,955
Total securities available-for-sale	$	5,243,681	$	945	$	(511,864	)	$	4,732,762

The Company did not hold any securities classified as held-to-maturity at June 30, 2024, June 30, 2023, or December 31, 2023.

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 June 30, 2024 and 2023, and December 31, 2023, were computed by using scheduled amortization of balances and historical prepayment rates.

The amortized cost and estimated fair value of available-for-sale securities at June 30, 2024, by contractual and expected maturity, are shown below (dollars in thousands):


	Amortized		Estimated
	Cost Basis		Fair Value
Due within one year	$	304,065	$	299,230
Due after one year through five years		1,709,307		1,576,132
Due after five years through ten years		2,143,482		1,856,004
Due after ten years		975,597		841,658
Total	$	5,132,451	$	4,573,024

The following tables disclose as of June 30, 2024 and 2023, and December 31, 2023, 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
June 30, 2024	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	1,448	$	12	$	340,528	$	10,694	$	341,976	$	10,706
Obligations of states and political subdivisions		32,423		320		1,391,496		139,117	$	1,423,919		139,437
Residential mortgage-backed securities		80,096		462		2,183,346		389,031	$	2,263,442		389,493
Commercial mortgage-backed securities		92,487		928		257,535		11,054	$	350,022		11,982
Corporate bonds and other		—		—		104,031		8,300	$	104,031		8,300
Total	$	206,454	$	1,722	$	4,276,936	$	558,196	$	4,483,390	$	559,918


	Less than 12 Months				12 Months or Longer				Total
June 30, 2023	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	47,498	$	1,614	$	436,278	$	22,734	$	483,776	$	24,348
Obligations of states and political subdivisions		137,728		1,838		1,457,431		164,796		1,595,159		166,634
Residential mortgage-backed securities		68,439		3,609		2,403,837		399,151		2,472,276		402,760
Commercial mortgage-backed securities		99,347		4,771		215,040		12,671		314,387		17,442
Corporate bonds and other		38,042		1,282		64,152		9,031		102,194		10,313
Total	$	391,054	$	13,114	$	4,576,738	$	608,383	$	4,967,792	$	621,497


	Less than 12 Months				12 Months or Longer				Total
December 31, 2023	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	3,477	$	7	$	477,306	$	14,738	$	480,783	$	14,745
Obligations of states and political subdivisions		11,855		34		1,427,975		125,148		1,439,830		125,182
Residential mortgage-backed securities		1,631		1		2,361,089		352,882		2,362,720		352,883
Commercial mortgage-backed securities		—		—		284,324		11,339		284,324		11,339
Corporate bonds and other		—		—		104,955		7,715		104,955		7,715
Total	$	16,963	$	42	$	4,655,649	$	511,822	$	4,672,612	$	511,864

The number of investments in an unrealized loss position totaled 828 at June 30, 2024. 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 June 30, 2024 and 2023, and December 31, 2023, 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 June 30, 2024 and 2023, and December 31, 2023. Unrealized losses on investment securities are expected to recover over time as these securities approach maturity. Our mortgage related securities are backed by GNMA, FNMA and FHLMC or are collateralized by securities backed by these agencies. At June 30, 2024, 66.94% of our available-for-sale securities that are obligations of states and political subdivisions were issued within the State of Texas, of which 56.54% are guaranteed by the Texas Permanent School Fund.

Securities, carried at approximately $2,479,260,000 on June 30, 2024, 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 June 30, 2024, there were no sales of investment securities that were classified as available-for-sale. During the three-months ended June 30, 2023, sales of investment securities that were classified as available-for-sale were $61,339,000. There were no gross realized security gains or losses from sales and calls during the second quarter of 2024. Gross realized security gains from sales and calls during the second quarter of 2023 totaled $596,000. Gross realized security losses from sales or calls during the second quarter of 2023 totaled $550,000.

During the six-months ended June 30, 2024, there were no sales of investment securities that were classified as available-for-sale. During the six-months ended June 30, 2023, sales of investment securities that were classified as available-for-sale were $207,287,000. There were no gross realized security gains or losses from sales and calls during the six-months ended June 30, 2024. Gross realized security gains from sales and calls during the six-months ended June 30, 2023 totaled $1,648,000. Gross realized security losses from sales or calls during the six-months ended June 30, 2023 totaled $1,590,000

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