The following tables detail the amortized cost, allowance for credit losses and the estimated fair value of the Company's investments in available-for-sale and held-to-maturity debt securities. None of the Company's investments in debt securities are classified as trading.


	September 30, 2025
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
Collateralized mortgage obligations (CMO)	$	490,692	$	425	$	74,326	$	—	$	416,791
Fannie Mae (FNMA) mortgage-backed securities (MBS)	3,154,279		1,892		410,013		—		2,746,158
Freddie Mac (FHLMC) MBS	117,850		54		8,357		—		109,547
Ginnie Mae (GNMA) MBS	45,594		44		2,740		—		42,898
Government-sponsored enterprises (GSE) agency notes	220,940		—		34,175		—		186,765
	$	4,029,355	$	2,415	$	529,611	$	—	$	3,502,159
Held-to-Maturity Debt Securities(1)
FNMA MBS	$	799,548	$	—	$	92,293	$	—	$	707,255
State and political subdivisions	180,156		504		1,727		6		178,927

	$	979,704	$	504	$	94,020	$	6	$	886,182

(1)Held-to-maturity securities transferred from available-for-sale are included in held-to-maturity at fair value basis at the time of transfer. The amortized cost of transferred held-to-maturity securities included net unrealized losses of $87.6 million at September 30, 2025, which are offset in Accumulated other comprehensive loss. At the time of transfer, there was no allowance for credit loss on the available-for-sale securities. Subsequent to transfer, the securities were evaluated for credit loss.


	December 31, 2024
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
CMO	$	526,796	$	113	$	95,967	$	—	$	430,942
FNMA MBS	3,305,418		172		550,011		—		2,755,579
FHLMC MBS	118,605		—		13,091		—		105,514
GNMA MBS	44,578		—		3,902		—		40,676
GSE agency notes	222,869		—		44,932		—		177,937
	$	4,218,266	$	285	$	707,903	$	—	$	3,510,648
Held-to-Maturity Debt Securities(1)
FNMA MBS	$	831,325	$	—	$	116,600	$	—	$	714,725
State and political subdivisions	183,843		247		3,297		7		180,786

	$	1,015,168	$	247	$	119,897	$	7	$	895,511

(1)Held-to-maturity securities transferred from available-for-sale are included in held-to-maturity at fair value at the time of transfer. The amortized cost of transferred held-to-maturity securities included net unrealized losses of $100.5 million at December 31, 2024, which are offset in Accumulated other comprehensive loss. At the time of transfer, there was no allowance for credit loss on the available-for-sale securities. Subsequent to transfer, the securities were evaluated for credit loss.

The scheduled maturities of available-for-sale debt securities at September 30, 2025 and December 31, 2024 are presented in the table below:


	Available-for-Sale
	Amortized		Fair
(Dollars in thousands)	Cost		Value
September 30, 2025 (1)
Within one year	$	46,291	$	45,761
After one year but within five years	158,811		150,121
After five years but within ten years	483,677		429,792
After ten years	3,340,576		2,876,485
	$	4,029,355	$	3,502,159
December 31, 2024 (1)
Within one year	$	16,833	$	16,698
After one year but within five years	147,157		138,870
After five years but within ten years	487,921		409,908
After ten years	3,566,355		2,945,172
	$	4,218,266	$	3,510,648

As of September 30, 2025, the Company’s available-for-sale investment securities consisted of 1,009 securities, 954 of which were in an unrealized loss position, and substantially all of the Company's available-for-sale investment securities were mortgage-backed securities or collateral mortgage obligations which were issued or guaranteed by U.S. government-sponsored entities and agencies. As of September 30, 2025 and December 31, 2024, there were no holdings of securities of any one issuer, other than the U.S. government and its agencies, in an amount greater than 10% of shareholders’ equity.


	Held-to-Maturity
	Amortized		Fair
(Dollars in thousands)	Cost		Value
September 30, 2025 (1)
Within one year	$	1,420	$	1,420
After one year but within five years	19,175		19,163
After five years but within ten years	68,957		68,957
After ten years	890,152		796,642
	$	979,704	$	886,182
December 31, 2024 (1)
Within one year	$	—	$	—
After one year but within five years	16,727		16,444
After five years but within ten years	51,671		50,451
After ten years	946,770		828,616
	$	1,015,168	$	895,511

MBS may have expected maturities that differ from their contractual maturities. These differences arise because issuers may have the right to call securities and borrowers may have the right to prepay obligations with or without prepayment penalty.

The held-to-maturity debt securities are not collateral-dependent securities as these are general obligation bonds issued by cities, states, counties, or other local governments, and government-sponsored MBS.

Investment securities with fair market values aggregating $3.7 billion and $3.3 billion were pledged as collateral for investment sweep repurchase agreements, municipal deposits, and other obligations as of September 30, 2025 and December 31, 2024, respectively.

As of September 30, 2025 and December 31, 2024, the Company's debt securities portfolio had remaining unamortized premiums of $42.1 million and $48.1 million, respectively, and unaccreted discounts of $17.1 million and $17.6 million, respectively.

For debt securities in an unrealized loss position, the table below shows the gross unrealized losses and fair value by investment category and length of time that individual debt securities were in a continuous unrealized loss position at September 30, 2025.


	Duration of Unrealized Loss Position
	Less than 12 months				12 months or longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(Dollars in thousands)	Value		Loss		Value		Loss		Value		Loss
Available-for-sale debt securities:
CMO	$	—	$	—	$	406,409	$	74,326	$	406,409	$	74,326
FNMA MBS	36,195		167		2,598,550		409,846		2,634,745		410,013
FHLMC MBS	—		—		104,548		8,357		104,548		8,357
GNMA MBS	4,450		116		35,184		2,624		39,634		2,740
GSE agency notes	—		—		186,765		34,175		186,765		34,175
	$	40,645	$	283	$	3,331,456	$	529,328	$	3,372,101	$	529,611


	Duration of Unrealized Loss Position
	Less than 12 months				12 months or longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(Dollars in thousands)	Value		Loss		Value		Loss		Value		Loss
Available-for-sale debt securities:
CMO	$	—	$	—	$	420,663	$	95,967	$	420,663	$	95,967
FNMA MBS	46,971		525		2,691,778		549,486		2,738,749		550,011
FHLMC MBS	6		—		105,508		13,091		105,514		13,091
GNMA MBS	4,404		143		35,054		3,759		39,458		3,902
GSE agency notes	—		—		177,937		44,932		177,937		44,932
	$	51,381	$	668	$	3,430,940	$	707,235	$	3,482,321	$	707,903

The Company does not have the intent to sell, nor is it more likely than not it will be required to sell these securities before it is able to recover the amortized cost basis. The unrealized losses are the result of changes in market interest rates subsequent to purchase, not credit loss, as these are highly rated agency securities with no expected credit loss, in the event of a default. As a result, there is no allowance for credit losses recorded for available-for-sale debt securities as of September 30, 2025.

At September 30, 2025 and December 31, 2024, held-to-maturity debt securities had an amortized cost basis of $1.0 billion. The held-to-maturity debt security portfolio primarily consists of mortgage-backed securities which were issued or guaranteed by U.S. government-sponsored entities and agencies and highly rated municipal bonds. The Company monitors credit quality of its non-government and non-agency securities through credit ratings. The following table summarizes the amortized cost of debt securities held-to-maturity as of September 30, 2025, aggregated by credit quality indicator:


(Dollars in thousands)	FNMA MBS		State and political subdivisions
A+ rated or higher	$	—	$	180,156
Not rated	799,548		—
Ending balance	$	799,548	$	180,156


(Dollars in thousands)	FNMA MBS		State and political subdivisions
A+ rated or higher	$	—	$	183,843
Not rated	831,325		—
Ending balance	$	831,325	$	183,843

The Company reviewed its held-to-maturity debt securities by major security type for potential credit losses. There was no activity in the allowance for credit losses for FNMA MBS debt securities for the nine months ended September 30, 2025 and 2024. The following table presents the activity in the allowance for credit losses for state and political subdivisions debt securities for the three and nine months ended September 30, 2025 and 2024:


	Three months ended September 30,				Nine months ended September 30,
(Dollars in thousands)	2025		2024		2025		2024
Allowance for credit losses:
Beginning balance	$	6	$	7	$	7	$	8

Release of credit losses	—		—		(1)		(1)



Ending balance	$	6	$	7	$	6	$	7

Accrued interest receivable of $3.0 million and $3.6 million as of September 30, 2025 and December 31, 2024, respectively, for held-to-maturity debt securities were excluded from the evaluation of allowance for credit losses. There were no nonaccrual or past due held-to-maturity debt securities as of September 30, 2025 and December 31, 2024.