Securities

12 Months Ended

Dec. 31, 2021

Cash And Cash Equivalents [Abstract]

2. SECURITIES:

Debt securities have been classified in the condensed 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):


	December 31, 2021
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
Securities available-for-sale:
U.S. Treasury securities	$	126,716	$	125	$	—		$	126,841
Obligations of state and political subdivisions		2,638,369		116,319		(1,217	)		2,753,471
Residential mortgage-backed securities		3,256,746		23,990		(21,287	)		3,259,449
Commercial mortgage-backed securities		356,207		8,914		(1	)		365,120
Corporate bonds and other		69,472		32		(1,206	)		68,298
Total securities available-for-sale	$	6,447,510	$	149,380	$	(23,711	)	$	6,573,179


	December 31, 2020
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
Securities available-for-sale:
Obligations of state and political subdivisions	$	2,283,616	$	143,339	$	(79	)	$	2,426,876
Residential mortgage-backed securities		1,421,922		50,473		(115	)		1,472,280
Commercial mortgage-backed securities		467,243		22,077		(4	)		489,316
Corporate bonds and other		4,398		159		—			4,557
Total securities available-for-sale	$	4,177,179	$	216,048	$	(198	)	$	4,393,029

The Company did not hold any securities classified as held-to-maturity for the years ended December 31, 2021 and 2020.

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 December 31, 2021, 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 December 31, 2021, by contractual maturity, are shown below (in thousands):


	Amortized Cost Basis		Estimated Fair Value
Due within one year	$	261,110	$	264,173
Due after one year through five years		3,087,180		3,150,010
Due after five years through ten years		2,771,160		2,831,581
Due after ten years		328,060		327,415
Total	$	6,447,510	$	6,573,179

The following tables disclose, as of December 31, 2021 and 2020, 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 (in thousands):


	Less than 12 Months				12 Months or Longer				Total
December 31, 2021	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of state and political subdivisions	$	163,698	$	1,096	$	18,943	$	122	$	182,641	$	1,218
Residential mortgage-backed securities		2,263,010		19,742		54,392		1,544		2,317,402		21,286
Commercial mortgage-backed securities		820		1		—		—		820		1
Corporate bonds and other		47,436		635		16,432		571		63,868		1,206
Total	$	2,474,964	$	21,474	$	89,767	$	2,237	$	2,564,731	$	23,711


	Less than 12 Months				12 Months or Longer				Total
December 31, 2020	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Obligations of state and political subdivisions	$	25,214	$	79	$	—	$	—	$	25,214	$	79
Residential mortgage-backed securities		36,017		96		3,156		19		39,173		115
Commercial mortgage-backed securities		16,218		4		—		—		16,218		4
Total	$	77,449	$	179	$	3,156	$	19	$	80,605	$	198

The number of investments in an unrealized loss position totaled 135 at December 31, 2021. Any unrealized losses in the U.S. treasuries and government agencies, state and municipal, mortgage-backed and asset-backed investment securities at December 31, 2021 are due to changes in interest rates and not credit-related events. As such, no allowance for credit losses is required at December 31, 2021. 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 December 31, 2021 and 2020, 72.72% and 80.87%, respectively, of our available-for-sale securities that are obligations of states and political subdivisions were issued within the State of Texas, of which 53.94% and 51.57%, respectively, were guaranteed by the Texas Permanent School Fund.

Securities, carried at approximately $3,644,626,000 and $3,005,084,000 December 31, 2021 and 2020, respectively, were pledged as collateral for public or trust fund deposits, repurchase agreements and for other purposes required or permitted by law.

During 2021, 2020 and 2019, sales of investment securities that were classified as available-for-sale totaled $10,631,000, $263,042,000 and $67,414,000. Gross realized gains from 2021, 2020 and 2019, securities sales and calls were $815,000, $3,637,000 and $752,000, respectively. There were no gross realized losses from security sales and calls during 2021. Gross realized losses from 2020 and 2019 securities sales and calls were $4,000 and $19,000, respectively. The specific identification method was used to determine cost in order to compute the realized gains and losses