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, 2022
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
Collateralized mortgage obligation (CMO)	$	608,834	$	—	$	102,454	$	—	$	506,380
Fannie Mae (FNMA) mortgage-backed securities (MBS)	3,823,036		—		572,778		—		3,250,258
Freddie Mac (FHLMC) MBS	135,554		—		13,555		—		121,999
Ginnie Mae (GNMA) MBS	39,116		—		2,978		—		36,138
Government-sponsored enterprises (GSE) agency notes	228,010		—		49,725		—		178,285
	$	4,834,550	$	—	$	741,490	$	—	$	4,093,060
Held-to-Maturity Debt Securities(1)
FNMA MBS	$	909,498	$	—	$	68,677	$	—	$	840,821
State and political subdivisions	201,631		532		3,372		10		198,781
Foreign bonds	500		2		—		—		502
	$	1,111,629	$	534	$	72,049	$	10	$	1,040,104

(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 $142.8 million at December 31, 2022, which are offset in Accumulated other comprehensive income (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, 2021
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
CMO	$	586,830	$	3,569	$	14,633	$	—	$	575,766
FNMA MBS	4,275,307		24,170		53,793		—		4,245,684
FHLMC MBS	139,708		6,336		516		—		145,528
GNMA MBS	17,456		551		71		—		17,936
GSE agency notes	230,581		—		10,184		—		220,397
	$	5,249,882	$	34,626	$	79,197	$	—	$	5,205,311
Held-to-Maturity Debt Securities(1)
State and political subdivisions	$	90,146	$	3,489	$	—	$	4	$	93,631
Foreign bonds	500		—		—		—		500
	$	90,646	$	3,489	$	—	$	4	$	94,131

(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 gains of $0.2 million at December 31, 2021, which are offset in Accumulated other comprehensive income (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, 2022 (1)
Within one year	$	—	$	—
After one year but within five years	83,014		77,499
After five years but within ten years	465,777		398,607
After ten years	4,285,759		3,616,954
	$	4,834,550	$	4,093,060
December 31, 2021 (1)
Within one year	$	—	$	—
After one year but within five years	103,960		107,009
After five years but within ten years	204,186		204,289
After ten years	4,941,736		4,894,013
	$	5,249,882	$	5,205,311

As of December 31, 2022, the Company’s available-for-sale investment securities consisted of 958 securities, 955 of which were in an unrealized loss position.

As of December 31, 2022, substantially all of the Corporation’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, 2022 and December 31, 2021, 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, 2022 (1)
Within one year	$	731	$	732
After one year but within five years	9,530		9,476
After five years but within ten years	46,170		45,944
After ten years	1,055,198		983,952
	$	1,111,629	$	1,040,104
December 31, 2021 (1)
Within one year	$	232	$	234
After one year but within five years	2,675		2,736
After five years but within ten years	44,137		45,404
After ten years	43,602		45,757
	$	90,646	$	94,131

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, 2022.

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.

During the second quarter of 2022, the Company transferred investment securities with a book value of $1.1 billion from available-for-sale to held-to-maturity to mitigate the impact of the rising interest rate environment to Accumulated other comprehensive income (loss) in the Company's Consolidated Statement of Changes in Stockholders' Equity. The transfer occurred at a fair value totaling $931.4 million. The amortized cost of transferred held-to-maturity securities included net unrealized losses of $157.6 million at June 30, 2022, which are offset in Accumulated other comprehensive income (loss). No gains or losses on these securities were recognized at the time of transfer.

Investment securities with fair market values aggregating $2.8 billion and $2.2 billion were pledged as collateral for investment sweep repurchase agreements, municipal deposits, and other obligations as of December 31, 2022 and December 31, 2021, respectively.

During the year ended December 31, 2022, the Company had no sales of debt securities categorized as available-for-sale. During the year ended December 31, 2021, the Company sold $14.1 million of debt securities categorized as available-for-sale, resulting in $0.3 million of realized gains and no realized losses. During the year ended December 31, 2020, the Company sold $305.8 million, resulting in realized gains of $9.1 million and no realized losses.

As of December 31, 2022 and December 31, 2021, the Company's debt securities portfolio had remaining unamortized premiums of $66.6 million and $69.4 million, respectively, and unaccreted discounts of $25.2 million and $12.7 million, respectively.

For debt securities in an unrealized loss position and an allowance has not been recorded, 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, 2022.


	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	$	158,449	$	13,855	$	347,931	$	88,599	$	506,380	$	102,454
FNMA MBS	1,237,560		145,752		2,012,698		427,026		3,250,258		572,778
FHLMC MBS	102,321		9,268		19,671		4,287		121,992		13,555
GNMA MBS	32,076		2,265		4,030		713		36,106		2,978
GSE agency notes	—		—		178,285		49,725		178,285		49,725
	$	1,530,406	$	171,140	$	2,562,615	$	570,350	$	4,093,021	$	741,490


	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	$	411,347	$	12,730	$	35,638	$	1,903	$	446,985	$	14,633
FNMA MBS	3,018,606		41,021		356,665		12,772		3,375,271		53,793
FHLMC MBS	11,227		348		1,917		168		13,144		516
GNMA MBS	4,847		71		—		—		4,847		71
GSE agency notes	64,509		1,918		155,888		8,266		220,397		10,184
	$	3,510,536	$	56,088	$	550,108	$	23,109	$	4,060,644	$	79,197

At December 31, 2022, available-for-sale debt securities for which the amortized cost basis exceeded fair value totaled $4.1 billion. Total unrealized losses on these securities were $741.5 million at December 31, 2022. 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 December 31, 2022.

At December 31, 2022 and December 31, 2021, held-to-maturity debt securities had an amortized cost basis of $1.1 billion and $90.6 million, 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.


(Dollars in thousands)	FNMA MBS		State and political subdivisions		Foreign bonds
A+ rated or higher	$	—	$	201,631	$	500
Not rated	909,498		—		—
Ending balance	$	909,498	$	201,631	$	500

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 and foreign bond debt securities for the twelve months ended December 31, 2022 and 2021. 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, 2022 and 2021:


	Twelve months ended December 31,
(Dollars in thousands)	2022		2021

Allowance for credit losses:
Beginning balance	$	4		$	6

Provision for credit losses	6			(2)



Ending balance	$	10		$	4

Accrued interest receivable of $2.4 million and $0.9 million as of December 31, 2022 and December 31, 2021, 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, 2022 and December 31, 2021.

During the twelve months ended December 31, 2022, total net gains on equity investments of $6.0 million were recorded from the Company's investment in Cred.ai in June 2022.

During the twelve months ended December 31, 2021, total net gains on equity investments of $4.4 million were recorded from the sale of the Company's investment in Social Finance, Inc. (SoFi) in July 2021. This included a net realized loss of $0.7 million which was recorded in Realized loss (gain) on equity investments, net in the Consolidated Statements of Income at the time of sale.