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.


	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
Collateralized mortgage obligations (CMO)	$	526,796	$	113	$	95,967	$	—	$	430,942
Fannie Mae (FNMA) mortgage-backed securities (MBS)	3,305,418		172		550,011		—		2,755,579
Freddie Mac (FHLMC) MBS	118,605		—		13,091		—		105,514
Ginnie Mae (GNMA) MBS	44,578		—		3,902		—		40,676
Government-sponsored enterprises (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 amortized cost basis 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.


	December 31, 2023
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
CMO	$	560,952	$	—	$	96,333	$	—	$	464,619
FNMA MBS	3,544,762		162		502,574		—		3,042,350
FHLMC MBS	126,856		—		11,324		—		115,532
GNMA MBS	46,333		6		2,999		—		43,340
GSE agency notes	225,439		—		44,743		—		180,696
	$	4,504,342	$	168	$	657,973	$	—	$	3,846,537
Held-to-Maturity Debt Securities(1)
FNMA MBS	$	872,653	$	—	$	74,332	$	—	$	798,321
State and political subdivisions	185,912		2,665		959		8		187,610

	$	1,058,565	$	2,665	$	75,291	$	8	$	985,931

(1)Held-to–maturity securities transferred from available-for-sale are included in held-to-maturity at amortized cost basis at the time of transfer. The amortized cost of transferred held-to-maturity securities included net unrealized losses of $120.4 million at December 31, 2023, 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.


	Available-for-Sale
(Dollars in thousands)	Amortized Cost		Fair Value
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
December 31, 2023 (1)
Within one year	$	—	$	—
After one year but within five years	86,224		82,387
After five years but within ten years	569,956		485,593
After ten years	3,848,162		3,278,557
	$	4,504,342	$	3,846,537

As of December 31, 2024, 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 December 31, 2024 and December 31, 2023, 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
(Dollars in thousands)	Amortized Cost		Fair Value
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
December 31, 2023 (1)
Within one year	$	—	$	—
After one year but within five years	10,932		10,856
After five years but within ten years	46,489		46,246
After ten years	1,001,144		928,829
	$	1,058,565	$	985,931

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 estimated weighted average duration of MBS was 5.9 years at December 31, 2024.

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 and foreign governments.

Investment securities with fair market values aggregating $3.3 billion were pledged as collateral for investment sweep repurchase agreements, municipal deposits, and other obligations as of December 31, 2024 and December 31, 2023.

As of December 31, 2024 and December 31, 2023, the Company's debt securities portfolio had remaining unamortized premiums of $48.1 million and $56.9 million, respectively, and unaccreted discounts of $17.6 million and $20.9 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 December 31, 2024.


	Duration of Unrealized Loss Position
	Less than 12 months				12 months or longer				Total
(Dollars in thousands)	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized 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


	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	$	—	$	—	$	464,619	$	96,333	$	464,619	$	96,333
FNMA MBS	9,068		125		3,026,520		502,449		3,035,588		502,574
FHLMC MBS	—		—		115,525		11,324		115,525		11,324
GNMA MBS	10,543		217		31,681		2,782		42,224		2,999
GSE agency notes	—		—		180,696		44,743		180,696		44,743
	$	19,611	$	342	$	3,819,041	$	657,631	$	3,838,652	$	657,973

At December 31, 2024, available-for-sale debt securities for which the amortized cost basis exceeded fair value totaled $3.5 billion. Total unrealized losses on these securities were $707.9 million at December 31, 2024. The Company assessed whether an allowance for credit losses was required on our available-for-sale debt securities and determined no allowance was necessary as of December 31, 2024 as (1) the Company currently 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 and (2) 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.

At December 31, 2024 and December 31, 2023, held-to-maturity debt securities had an amortized cost basis of $1.0 billion and $1.1 billion, respectively. 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 debt securities through credit ratings.

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 twelve months ended December 31, 2024 and 2023. The following table presents the activity in the allowance for credit losses for state and political subdivisions debt securities for the twelve months ended December 31, 2024, 2023, and 2022:


	Twelve months ended December 31,
(Dollars in thousands)	2024		2023	2022

Allowance for credit losses:
Beginning balance	$	8		$	10	$	4

Provision for credit losses	(1)			(2)		6



Ending balance	$	7		$	8	$	10

Accrued interest receivable of $3.6 million and $3.7 million as of December 31, 2024 and December 31, 2023, 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 December 31, 2024 and December 31, 2023.

During the year ended December 31, 2024, total net gains on equity investments of $2.3 million were recorded, driven by an annual earnout distribution related to the Company's investment in Spring EQ presented within Realized gain on sale of equity investment, net in the Consolidated Statements of Income.

During the year ended December 31, 2023, total net gains on equity investments of $9.8 million were recorded, driven by a realized gain on the Company's investment in Spring EQ presented within Realized gain on sale of equity investment, net in the Consolidated Statements of Income. During the year ended December 31, 2023, the Company recognized $2.5 million of net gains related to our equity method investments within Other income on the Consolidated Statements of Income.