Securities

6 Months Ended

Jun. 30, 2023

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, 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


	June 30, 2022
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	501,098	$	12	$	(14,752	)	$	486,358
Obligations of states and political subdivisions		2,419,232		7,737		(182,365	)		2,244,604
Residential mortgage-backed securities		3,265,654		399		(301,149	)		2,964,904
Commercial mortgage-backed securities		423,168		476		(8,819	)		414,825
Corporate bonds and other		113,184		88		(8,927	)		104,345
Total securities available-for-sale	$	6,722,336	$	8,712	$	(516,012	)	$	6,215,036


	December 31, 2022
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost Basis		Holding Gains		Holding Losses			Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	508,275	$	11	$	(25,737	)	$	482,549
Obligations of states and political subdivisions		2,104,193		1,217		(206,799	)		1,898,611
Residential mortgage-backed securities		3,034,120		8		(417,562	)		2,616,566
Commercial mortgage-backed securities		392,914		1		(18,046	)		374,869
Corporate bonds and other		112,846		-		(11,082	)		101,764
Total securities available-for-sale	$	6,152,348	$	1,237	$	(679,226	)	$	5,474,359

The Company did not hold any securities classified as held-to-maturity at June 30, 2023, June 30, 2022, or December 31, 2022.

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, 2023 and 2022, and December 31, 2022, 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, 2023, by contractual and expected maturity, are shown below (dollars in thousands):


	Amortized		Estimated
	Cost Basis		Fair Value
Due within one year	$	326,804	$	320,734
Due after one year through five years		1,487,053		1,379,040
Due after five years through ten years		2,817,340		2,473,140
Due after ten years		1,056,155		893,348
Total	$	5,687,352	$	5,066,262

The following tables disclose as of June 30, 2023 and 2022, and December 31, 2022, 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, 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
June 30, 2022	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	466,438	$	14,752	$	—	$	—	$	466,438	$	14,752
Obligations of states and political subdivisions		1,623,146		178,446		24,038		3,919		1,647,184		182,365
Residential mortgage-backed securities		2,631,511		266,352		277,404		34,797		2,908,915		301,149
Commercial mortgage-backed securities		341,997		8,819		—		—		341,997		8,819
Corporate bonds and other		73,358		4,287		26,397		4,640		99,755		8,927
Total	$	5,136,450	$	472,656	$	327,839	$	43,356	$	5,464,289	$	516,012


	Less than 12 Months				12 Months or Longer				Total
December 31, 2022	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
U.S. Treasury securities	$	307,012	$	11,650	$	173,105	$	14,087	$	480,117	$	25,737
Obligations of states and political subdivisions		770,469		55,943		946,571		150,856		1,717,040		206,799
Residential mortgage-backed securities		470,970		37,065		2,143,869		380,497		2,614,839		417,562
Commercial mortgage-backed securities		319,303		11,677		54,862		6,369		374,165		18,046
Corporate bonds and other		41,920		1,698		59,844		9,384		101,764		11,082
Total	$	1,909,674	$	118,033	$	3,378,251	$	561,193	$	5,287,925	$	679,226

The number of investments in an unrealized loss position totaled 934 at June 30, 2023. 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, 2023 and 2022, and December 31, 2022, 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, 2023 and 2022, and December 31, 2022. 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, 2023, 69.19% of our available-for-sale securities that are obligations of states and political subdivisions were issued within the State of Texas, of which 52.59% are guaranteed by the Texas Permanent School Fund.

Securities, carried at approximately $3,447,659,000 on June 30, 2023, 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, 2023 and 2022, sales of investment securities that were classified as available-for-sale were $61,339,000 and $188,363,000, respectively. Gross realized security gains from sales and calls during the second quarter of 2023 and 2022 totaled $596,000 and $3,990,000, respectively. Gross realized security losses from sales or calls during the second quarter of 2023 or 2022 totaled $550,000 and $2,342,000, respectively.

During the six-months ended June 30, 2023 and 2022, sales of investment securities that were classified as available-for-sale were $207,287,000 and $188,363,000, respectively. Gross realized security gains from sales and calls during the six-months ended June 30, 2023 and 2022 totaled $1,648,000 and $4,023,000, respectively. Gross realized security losses from sales or calls during the six-months ended June 30, 2023 and 2022 totaled $1,590,000 and $2,344,000, respectively.

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