Securities (Tables)

9 Months Ended

Sep. 30, 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
September 30, 2023	(Dollars in thousands)
Mortgage backed securities (1)	$	7	$	—	$	—	$	7
States and political subdivisions		685		—		—		685
Other securities		500		—		—		500
Total	$	1,192	$	—	$	—	$	1,192
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
September 30, 2023	(Dollars in thousands)
U.S. treasuries	$	1,564,934	$	—	$	(96,730	)	$	1,468,204
U.S. federal agencies		12,427		156		(3	)		12,580
Mortgage backed securities (1)		16,877		7		(2,472	)		14,412
States and political subdivisions		10,115		5		(189	)		9,931
Asset backed securities		12,789		—		(378	)		12,411
Other securities		8,163		—		(1,445	)		6,718
Total	$	1,625,305	$	168	$	(101,217	)	$	1,524,256
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.

	September 30, 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	$	350	$	350	$	1,186	$	1,186
After one year but within five years		841		841		1,195		1,195
After five years but within ten years		1		1		2		2
After ten years		—		—		—		—
Total	$	1,192	$	1,192	$	2,383	$	2,383
Available for Sale
Contractual maturity of debt securities:
Within one year	$	208,397	$	203,774	$	101,607	$	100,655
After one year but within five years		1,317,661		1,228,720		1,316,874		1,233,725
After five years but within ten years		60,974		56,159		170,513		163,101
After ten years		38,273		35,603		42,897		40,740
Total debt securities	$	1,625,305	$	1,524,256	$	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:

	September 30, 2023		December 31, 2022
	(Dollars in thousands)
Book value of pledged securities	$	542,516	$	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:

	For the Nine Months Ended September 30,
	2023		2022
	(Dollars in thousands)
Proceeds	$	—	$	222,474
Gross losses realized		—		3,990

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 September 30, 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)
September 30, 2023
Available for Sale
U.S. treasuries		71	$	93,372	$	2,708	$	1,374,832	$	94,022	$	1,468,204	$	96,730
U.S. federal agencies		3		1,260		3		—		—		1,260		3
Mortgage backed securities		83		1,242		38		12,887		2,434		14,129		2,472
States and political subdivisions		9		1,657		21		1,292		168		2,949		189
Asset backed securities		1		—		—		12,411		378		12,411		378
Other securities		3		—		—		6,718		1,445		6,718		1,445
Total		170	$	97,531	$	2,770	$	1,408,140	$	98,447	$	1,505,671	$	101,217
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