Securities (Tables)

3 Months Ended

Mar. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Estimated Fair Values of Debt Securities Held for Investment

The following table summarizes the amortized cost and estimated fair values of debt securities held for investment:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
March 31, 2023	(Dollars in thousands)
Mortgage backed securities (1)	$	10	$	1	$	—	$	11
States and political subdivisions		1,810		—		—		1,810
Other securities		500		—		—		500
Total	$	2,320	$	1	$	—	$	2,321
December 31, 2022
Mortgage backed securities (1)	$	13	$	—	$	—	$	13
States and political subdivisions		1,870		—		—		1,870
Other securities		500		—		—		500
Total	$	2,383	$	—	$	—	$	2,383

Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale

The following table summarizes the amortized cost and estimated fair values of debt securities available for sale:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
March 31, 2023	(Dollars in thousands)
U.S. treasuries	$	1,629,245	$	1,341	$	(72,992	)	$	1,557,594
U.S. federal agencies		14,072		183		(1	)		14,254
Mortgage backed securities (1)		17,934		26		(1,773	)		16,187
States and political subdivisions		8,236		33		(114	)		8,155
Asset backed securities		12,780		—		(417	)		12,363
Other securities		8,163		—		(803	)		7,360
Total	$	1,690,430	$	1,583	$	(76,100	)	$	1,615,913
December 31, 2022
U.S. treasuries	$	1,568,563	$	—	$	(90,699	)	$	1,477,864
U.S. federal agencies		15,025		198		(1	)		15,222
Mortgage backed securities (1)		18,449		21		(1,884	)		16,586
States and political subdivisions		8,320		35		(221	)		8,134
Asset backed securities		13,371		—		(361	)		13,010
Other securities		8,163		—		(758	)		7,405
Total	$	1,631,891	$	254	$	(93,924	)	$	1,538,221

(1) Primarily consists of FHLMC, FNMA, GNMA and mortgage backed securities through U.S. agencies.

Maturity of Debt Securities

The maturities of debt securities held for investment and available for sale are summarized in the following table using contractual maturities. Actual maturities may differ from contractual maturities due to obligations that are called or prepaid. For purposes of the maturity table, mortgage-backed securities, which are not due at a single maturity date, have been presented at their contractual maturity.

	March 31, 2023				December 31, 2022
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(Dollars in thousands)
Held for Investment
Contractual maturity of debt securities:
Within one year	$	1,186	$	1,186	$	1,186	$	1,186
After one year but within five years		1,132		1,133		1,195		1,195
After five years but within ten years		2		2		2		2
After ten years		—		—		—		—
Total	$	2,320	$	2,321	$	2,383	$	2,383
Available for Sale
Contractual maturity of debt securities:
Within one year	$	105,557	$	104,164	$	101,607	$	100,655
After one year but within five years		1,336,179		1,267,384		1,316,874		1,233,725
After five years but within ten years		207,450		205,173		170,513		163,101
After ten years		41,244		39,192		42,897		40,740
Total debt securities	$	1,690,430	$	1,615,913	$	1,631,891	$	1,538,221

Company's Book Value of Pledged Debt Securities

The following table is a summary of the Company’s book value of securities that were pledged as collateral for public funds on deposit, repurchase agreements and for other purposes as required or permitted by law:

	March 31, 2023		December 31, 2022
	(Dollars in thousands)
Book value of pledged securities	$	580,946	$	573,952

Proceeds from Sales and Realized Losses on Available foe Sale Debt Securities

The following is a detail of proceeds from sales and the realized losses on available for sale debt securities:

	March 31, 2023		March 31, 2022
	(Dollars in thousands)
Proceeds	$	—	$	222,473
Gross losses realized		—		3,990

There were no sales of debt securities and therefore no proceeds from sales or realized securities gains or losses on available for sale debt securities for the three months ended March 31, 2023.

Summary of Debt Securities with Unrealized Losses, Segregated by Duration of Unrealized Loss

The following table summarizes debt securities with unrealized losses, segregated by the duration of the unrealized loss, at March 31, 2023 and December 31, 2022 respectively:

			Less than 12 Months				More than 12 Months				Total
	Number of investments		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
			(Dollars in thousands)
March 31, 2023
Available for Sale
U.S. treasuries		71	$	501,386	$	9,684	$	958,843	$	63,308	$	1,460,229	$	72,992
U.S. federal agencies		1		344		1		—		—		344		1
Mortgage backed securities		95		302		3		14,364		1,770		14,666		1,773
States and political subdivisions		8		1,486		14		1,311		100		2,797		114
Asset backed securities		1		—		—		12,363		417		12,363		417
Other securities		3		4,793		370		2,567		433		7,360		803
Total		179	$	508,311	$	10,072	$	989,448	$	66,028	$	1,497,759	$	76,100
December 31, 2022
Available for Sale
U.S. treasuries		74	$	787,925	$	27,078	$	689,939	$	63,621	$	1,477,864	$	90,699
U.S. federal agencies		1		—		—		349		1		349		1
Mortgage backed securities		92		10,001		1,239		5,055		645		15,056		1,884
States and political subdivisions		8		2,308		184		464		37		2,772		221
Asset backed securities		1		13,010		361		—		—		13,010		361
Other securities		3		4,871		291		2,534		467		7,405		758
Total		179	$	818,115	$	29,153	$	698,341	$	64,771	$	1,516,456	$	93,924