Securities (Tables)

12 Months Ended

Dec. 31, 2022

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
	(Dollars in thousands)
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
December 31, 2021
Mortgage backed securities (1)	$	32	$	1	$	—	$	33
States and political subdivisions		2,445		—		—		2,445
Other securities		500		—		—		500
Total	$	2,977	$	1	$	—	$	2,978

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
	(Dollars in thousands)
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
December 31, 2021
U.S. treasuries	$	455,701	$	3,693	$	(1,766	)	$	457,628
U.S. federal agencies		21,609		335		(2	)		21,942
Mortgage backed securities (1)		28,897		400		(14	)		29,283
States and political subdivisions		6,128		194		(3	)		6,319
Asset backed securities		13,354		3		—			13,357
Other securities		3,000		—		(6	)		2,994
Total	$	528,689	$	4,625	$	(1,791	)	$	531,523

(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.

	December 31,
	2022				2021
	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	$	577	$	577
After one year but within five years		1,195		1,195		2,396		2,397
After five years but within ten years		2		2		4		4
After ten years		—		—		—		—
Total	$	2,383	$	2,383	$	2,977	$	2,978
Available for Sale
Contractual maturity of debt securities:
Within one year	$	101,607	$	100,655	$	58,478	$	58,688
After one year but within five years		1,316,874		1,233,725		408,253		410,049
After five years but within ten years		170,513		163,101		10,851		11,011
After ten years		42,897		40,740		51,107		51,775
Total debt securities	$	1,631,891	$	1,538,221	$	528,689	$	531,523

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

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

	Year Ended December 31,
	2022		2021		2020
	(Dollars in thousands)
Proceeds	$	222,474	$	—	$	—
Gross losses realized		3,990		—		—

Company's Book Value of Pledged Debt Securities

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

	December 31,
	2022		2021
	(Dollars in thousands)
Book value of pledged securities	$	573,952	$	473,026

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 December 31, 2022 and 2021 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)
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
December 31, 2021
Available for Sale
U.S. treasuries		10	$	298,080	$	1,766	$	—	$	—	$	298,080	$	1,766
U.S. federal agencies		1		376		2		—		—		376		2
Mortgage backed securities		7		2,824		14		—		—		2,824		14
States and political subdivisions		2		505		3		—		—		505		3
Other securities		1		2,994		6		—		—		2,994		6
Total		21	$	304,779	$	1,791	$	—	$	—	$	304,779	$	1,791