Investment Securities (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Carrying Amounts of Securities and Their Approximate Fair Values

Investment securities have been classified in the unaudited consolidated balance sheets according to management’s intent. The carrying amounts of securities and their approximate fair values were as follows:

	September 30, 2023									December 31, 2022
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(dollars in thousands)
Available for sale securities
U.S. Government Sponsored    Enterprise obligations	$	22,998	$	—	$	(3,512	)	$	19,486	$	22,997	$	—	$	(3,264	)	$	19,733
Mortgage-backed securities		144,905		1		(28,139	)		116,767		158,034		3		(25,354	)		132,683
Corporate debt securities		—		—		—			—		996		4		—			1,000
Total available for sale securities	$	167,903	$	1	$	(31,651	)	$	136,253	$	182,027	$	7	$	(28,618	)	$	153,416
Held to maturity securities
U.S. Treasury Notes	$	4,023	$	—	$	(43	)	$	3,980	$	3,970	$	—	$	(18	)	$	3,952
Mortgage-backed securities		890,160		2		(182,990	)		707,172		951,372		4		(157,208	)		794,168
Corporate debt securities		250		—		(4	)		246		250		—		(6	)		244
Municipal securities		86,158		—		(12,920	)		73,238		96,405		88		(9,271	)		87,222
Total held to maturity securities	$	980,591	$	2	$	(195,957	)	$	784,636	$	1,051,997	$	92	$	(166,503	)	$	885,586
Total	$	1,148,494	$	3	$	(227,608	)	$	920,889	$	1,234,024	$	99	$	(195,121	)	$	1,039,002

Gross Unrealized Losses of Aggregated by Investment Category and Length of Time that Individual Investment Securities have been in Continuous Loss Position

The following tables show the Company’s investment securities with gross unrealized losses for which an allowance for credit losses has not been recorded at September 30, 2023 or at December 31, 2022, aggregated by investment category and length of time that individual investment securities have been in a continuous loss position:

	September 30, 2023
	Less than 12 months					12 months or longer					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(dollars in thousands)
Available for sale securities
U.S. Government Sponsored Enterprise    obligations	$	—	$	—		$	19,486	$	(3,512	)	$	19,486	$	(3,512	)
Mortgage-backed securities		170		(5	)		116,498		(28,134	)		116,668		(28,139	)
Total available for sale securities	$	170	$	(5	)	$	135,984	$	(31,646	)	$	136,154	$	(31,651	)
Held to maturity securities
U.S. Treasury Notes	$	3,980	$	(43	)	$	—	$	—		$	3,980	$	(43	)
Mortgage-backed securities		—		—			706,702		(182,990	)		706,702		(182,990	)
Corporate debt securities		—		—			246		(4	)		246		(4	)
Municipal securities		31,670		(1,420	)		41,568		(11,500	)		73,238		(12,920	)
Total held to maturity securities	$	35,650	$	(1,463	)	$	748,516	$	(194,494	)	$	784,166	$	(195,957	)
Total	$	35,820	$	(1,468	)	$	884,500	$	(226,140	)	$	920,320	$	(227,608	)

	December 31, 2022
	Less than 12 months					12 months or longer					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(dollars in thousands)
Available for sale securities
U.S. Government Sponsored Enterprise    obligations	$	10,722	$	(2,278	)	$	9,012	$	(986	)	$	19,734	$	(3,264	)
Mortgage-backed securities		41,832		(3,097	)		90,545		(22,257	)		132,377		(25,354	)
Total available for sale securities	$	52,554	$	(5,375	)	$	99,557	$	(23,243	)	$	152,111	$	(28,618	)
Held to maturity securities
U.S. Treasury Notes	$	3,952	$	(18	)	$	—	$	—		$	3,952	$	(18	)
Mortgage-backed securities		230,708		(22,362	)		562,835		(134,846	)		793,543		(157,208	)
Corporate debt securities		243		(6	)		—		—			243		(6	)
Municipal securities		51,969		(4,388	)		13,714		(4,883	)		65,683		(9,271	)
Total held to maturity securities	$	286,872	$	(26,774	)	$	576,549	$	(139,729	)	$	863,421	$	(166,503	)
Total	$	339,426	$	(32,149	)	$	676,106	$	(162,972	)	$	1,015,532	$	(195,121	)

Schedule of Amortized Cost and Fair Value of Debt Securities, Aggregated By Earlier of Guaranteed Call Date or Contractual Maturity

The amortized cost and fair value of debt securities, aggregated by the earlier of call date or contractual maturity, are shown below. Maturities of mortgage-backed securities do not take into consideration scheduled amortization or prepayments. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties.

	September 30, 2023
	Within One Year				After One, But Within Five Years				After Five, But Within Ten Years				After Ten Years				Total
	Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value
	(dollars in thousands)
Available for sale securities
U.S. Government Sponsored Enterprise obligations	$	—	$	—	$	9,998	$	9,139	$	5,000	$	4,243	$	8,000	$	6,104	$	22,998	$	19,486
Mortgage-backed securities		—		—		12,119		11,282		37,607		30,222		95,179		75,263		144,905		116,767
Corporate debt securities		—		—		—		—		—		—		—		—		—		—
Total available for sale securities	$	—	$	—	$	22,117	$	20,421	$	42,607	$	34,465	$	103,179	$	81,367	$	167,903	$	136,253
Held to maturity securities
U.S. Treasury Notes	$	3,064	$	3,040	$	959	$	940	$	—	$	—	$	—	$	—	$	4,023	$	3,980
Mortgage-backed securities		—		—		24,211		22,481		50,175		41,070		815,774		643,621		890,160		707,172
Corporate debt securities		250		246		—		—		—		—		—		—		250		246
Municipal securities		3,559		3,541		22,455		21,576		22,583		20,739		37,561		27,382		86,158		73,238
Total held to maturity securities	$	6,873	$	6,827	$	47,625	$	44,997	$	72,758	$	61,809	$	853,335	$	671,003	$	980,591	$	784,636
Total	$	6,873	$	6,827	$	69,742	$	65,418	$	115,365	$	96,274	$	956,514	$	752,370	$	1,148,494	$	920,889

Summary of Credit Rating of Debt Securities Portfolio

The following tables summarize the credit rating of the Company’s debt securities portfolio at September 30, 2023 and December 31, 2022.

	September 30, 2023
	Mortgage-backed Securities (1)		Corporate Debt Securities		Municipal Securities		U.S. GSE Obligations		U.S. Treasury Notes		Total
	(dollars in thousands)
Available for sale securities, at fair value
AAA/AA/A	$	116,767	$	—	$	—	$	19,486	$	—	$	136,253
Total available for sale securities	$	116,767	$	—	$	—	$	19,486	$	—	$	136,253
Held to maturity securities, at amortized cost
AAA/AA/A	$	890,160	$	250	$	86,158	$	—	$	4,023	$	980,591
Total held to maturity securities	$	890,160	$	250	$	86,158	$	—	$	4,023	$	980,591

	December 31, 2022
	Mortgage-backed Securities (1)		Corporate Debt Securities		Municipal Securities		U.S. GSE Obligations		U.S. Treasury Notes		Total
	(dollars in thousands)
Available for sale securities, at fair value
AAA/AA/A	$	132,683	$	—	$	—	$	19,733	$	—	$	152,416
BBB/BB/B		—		1,000		—		—		—		1,000
Total available for sale securities	$	132,683	$	1,000	$	—	$	19,733	$	—	$	153,416
Held to maturity securities, at amortized cost
AAA/AA/A	$	951,372	$	250	$	96,405	$	—	$	3,970	$	1,051,997
Total held to maturity securities	$	951,372	$	250	$	96,405	$	—	$	3,970	$	1,051,997

(1)Includes agency mortgage-backed pass-through securities and collateralized mortgage obligations issued by U.S. Government Sponsored Enterprises (“GSEs”) and U.S. government agencies, such as FNMA, FHLMC, and GNMA that are not rated by Moody’s or Standard & Poor's. Each security contains a guarantee by the issuing U.S. GSE or agency and therefore carries an implicit guarantee of the U.S. government. These have been categorized as AAA/AA/A.