Securities (Tables)

6 Months Ended

Jun. 30, 2025

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, 2025	(Dollars in thousands)
Mortgage backed securities (1)	$	1	$	—	$	—	$	1
States and political subdivisions		60		—		—		60
Other securities		500		—		—		500
Total	$	561	$	—	$	—	$	561
December 31, 2024
Mortgage backed securities (1)	$	2	$	—	$	—	$	2
States and political subdivisions		335		—		—		335
Other securities		500		—		—		500
Total	$	837	$	—	$	—	$	837

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, 2025	(Dollars in thousands)
U.S. treasuries	$	1,091,549	$	699	$	(21,223	)	$	1,071,025
U.S. federal agencies		7,432		74		(5	)		7,501
Mortgage backed securities (1)		14,030		9		(1,469	)		12,570
States and political subdivisions		5,874		2		(127	)		5,749
Other securities		8,163		—		(965	)		7,198
Total	$	1,127,048	$	784	$	(23,789	)	$	1,104,043
December 31, 2024
U.S. treasuries	$	1,216,258	$	—	$	(40,249	)	$	1,176,009
U.S. federal agencies		8,170		68		(6	)		8,232
Mortgage backed securities (1)		14,807		9		(1,772	)		13,044
States and political subdivisions		6,570		6		(140	)		6,436
Other securities		8,163		—		(967	)		7,196
Total	$	1,253,968	$	83	$	(43,134	)	$	1,210,917

(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, 2025				December 31, 2024
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(Dollars in thousands)
Held for Investment
Contractual maturity of debt securities:
Within one year	$	560	$	560	$	776	$	776
After one year but within five years		1		1		61		61
After five years but within ten years		—		—		—		—
After ten years		—		—		—		—
Total	$	561	$	561	$	837	$	837
Available for Sale
Contractual maturity of debt securities:
Within one year	$	340,445	$	336,476	$	335,108	$	330,076
After one year but within five years		757,598		741,045		888,721		853,508
After five years but within ten years		13,414		12,423		13,369		12,354
After ten years		15,591		14,099		16,770		14,979
Total debt securities	$	1,127,048	$	1,104,043	$	1,253,968	$	1,210,917

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, 2025		December 31, 2024
	(Dollars in thousands)
Book value of pledged securities	$	858,120	$	918,523

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, 2025 and December 31, 2024 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, 2025
Available for Sale
U.S. treasuries		42	$	—	$	—	$	979,845	$	21,223	$	979,845	$	21,223
U.S. federal agencies		5		637		3		440		2		1,077		5
Mortgage backed securities		55		1,163		2		11,068		1,467		12,231		1,469
States and political subdivisions		4		801		1		758		126		1,559		127
Other securities		3		—		—		7,198		965		7,198		965
Total		109	$	2,601	$	6	$	999,309	$	23,783	$	1,001,910	$	23,789
December 31, 2024
Available for Sale
U.S. treasuries		51	$	89,867	$	1,030	$	1,086,142	$	39,219	$	1,176,009	$	40,249
U.S. federal agencies		5		681		4		500		2		1,181		6
Mortgage backed securities		63		1,214		15		11,498		1,757		12,712		1,772
States and political subdivisions		4		802		2		752		138		1,554		140
Other securities		3		—		—		7,196		967		7,196		967
Total		126	$	92,564	$	1,051	$	1,106,088	$	42,083	$	1,198,652	$	43,134