Securities (Tables)

6 Months Ended

Jun. 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
June 30, 2023	(Dollars in thousands)
Mortgage backed securities (1)	$	8	$	—	$	—	$	8
States and political subdivisions		685		—		—		685
Other securities		500		—		—		500
Total	$	1,193	$	—	$	—	$	1,193
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
June 30, 2023	(Dollars in thousands)
U.S. treasuries	$	1,599,593	$	—	$	(89,527	)	$	1,510,066
U.S. federal agencies		13,368		170		(2	)		13,536
Mortgage backed securities (1)		17,479		10		(1,869	)		15,620
States and political subdivisions		10,998		21		(133	)		10,886
Asset backed securities		12,784		—		(349	)		12,435
Other securities		8,163		—		(1,279	)		6,884
Total	$	1,662,385	$	201	$	(93,159	)	$	1,569,427
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.

	June 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		842		842		1,195		1,195
After five years but within ten years		1		1		2		2
After ten years		—		—		—		—
Total	$	1,193	$	1,193	$	2,383	$	2,383
Available for Sale
Contractual maturity of debt securities:
Within one year	$	150,837	$	147,496	$	101,607	$	100,655
After one year but within five years		1,269,157		1,187,686		1,316,874		1,233,725
After five years but within ten years		202,889		196,755		170,513		163,101
After ten years		39,502		37,490		42,897		40,740
Total debt securities	$	1,662,385	$	1,569,427	$	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:

	June 30, 2023		December 31, 2022
	(Dollars in thousands)
Book value of pledged securities	$	593,260	$	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 Six Months Ended June 30,
	2023		2022
	(Dollars in thousands)
Proceeds	$	—	$	222,473
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 June 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)
June 30, 2023
Available for Sale
U.S. treasuries		73	$	414,002	$	13,360	$	1,096,064	$	76,167	$	1,510,066	$	89,527
U.S. federal agencies		3		1,305		2		—		—		1,305		2
Mortgage backed securities		91		1,452		5		13,899		1,864		15,351		1,869
States and political subdivisions		10		2,029		22		1,251		111		3,280		133
Asset backed securities		1		—		—		12,435		349		12,435		349
Other securities		3		4,476		687		2,408		592		6,884		1,279
Total		181	$	423,264	$	14,076	$	1,126,057	$	79,083	$	1,549,321	$	93,159
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