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.


	March 31, 2023
(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)	$	598,648	$	—	$	92,512	$	—	$	506,136
Fannie Mae (FNMA) mortgage-backed securities (MBS)	3,755,800		—		519,977		—		3,235,823
Freddie Mac (FHLMC) MBS	133,514		—		11,425		—		122,089
Ginnie Mae (GNMA) MBS	42,869		4		2,631		—		40,242
Government-sponsored enterprises (GSE) agency notes	227,368		—		45,199		—		182,169
	$	4,758,199	$	4	$	671,744	$	—	$	4,086,459
Held-to-Maturity Debt Securities(1)
FNMA MBS	$	902,774	$	—	$	60,122	$	—	$	842,652
State and political subdivisions	192,034		2,023		844		9		193,204

	$	1,094,808	$	2,023	$	60,966	$	9	$	1,035,856

(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 $137.3 million at March 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.


	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
CMO	$	608,834	$	—	$	102,454	$	—	$	506,380
FNMA MBS	3,823,036		—		572,778		—		3,250,258
FHLMC MBS	135,554		—		13,555		—		121,999
GNMA MBS	39,116		—		2,978		—		36,138
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 fair value 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 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 March 31, 2023 and December 31, 2022 are presented in the table below:


	Available-for-Sale
	Amortized		Fair
(Dollars in thousands)	Cost		Value
March 31, 2023 (1)
Within one year	$	2,562	$	2,465
After one year but within five years	80,148		75,722
After five years but within ten years	555,909		476,621
After ten years	4,119,580		3,531,651
	$	4,758,199	$	4,086,459
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

As of March 31, 2023, the Company’s available-for-sale investment securities consisted of 959 securities, 953 of which were in an unrealized loss position.

As of March 31, 2023, 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 March 31, 2023 and December 31, 2022, 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
March 31, 2023 (1)
Within one year	$	231	$	230
After one year but within five years	9,015		8,998
After five years but within ten years	41,627		41,803
After ten years	1,043,935		984,825
	$	1,094,808	$	1,035,856
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

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 6.0 years at March 31, 2023.

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 $3.5 billion and $2.8 billion were pledged as collateral for investment sweep repurchase agreements, municipal deposits, and other obligations as of March 31, 2023 and December 31, 2022, respectively.

As of March 31, 2023 and December 31, 2022, the Company's debt securities portfolio had remaining unamortized premiums of $64.1 million and $66.6 million, respectively, and unaccreted discounts of $24.1 million and $25.2 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 March 31, 2023.


	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	$	52,883	$	2,417	$	453,253	$	90,095	$	506,136	$	92,512
FNMA MBS	356,825		17,485		2,878,998		502,492		3,235,823		519,977
FHLMC MBS	53,125		2,697		68,958		8,728		122,083		11,425
GNMA MBS	30,087		1,497		9,659		1,134		39,746		2,631
GSE agency notes	—		—		182,169		45,199		182,169		45,199
	$	492,920	$	24,096	$	3,593,037	$	647,648	$	4,085,957	$	671,744


	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	$	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

At March 31, 2023, debt securities for which the amortized cost basis exceeded fair value totaled $4.1 billion. Total unrealized losses on these securities were $671.7 million at March 31, 2023. 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 March 31, 2023.

At March 31, 2023 and December 31, 2022, held-to-maturity debt securities had an amortized cost basis of $1.1 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 debt securities through credit ratings. The following table summarizes the amortized cost of debt securities held-to-maturity as of March 31, 2023, aggregated by credit quality indicator:


(Dollars in thousands)	FNMA MBS		State and political subdivisions
A+ rated or higher	$	—	$	192,034
Not rated	902,774		—
Ending balance	$	902,774	$	192,034


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


	Three months ended March 31,
(Dollars in thousands)	2023		2022
Allowance for credit losses:
Beginning balance	$	10	$	4

Provision for credit losses	(1)		—



Ending balance	$	9	$	4

Accrued interest receivable of $1.9 million and $2.4 million as of March 31, 2023 and December 31, 2022, 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 March 31, 2023 and December 31, 2022.

During the three months ended March 31, 2023, the Company recognized net losses related to our equity method investments of $1.3 million within Other income on the unaudited Consolidated Statements of Income. During the three months ended March 31, 2022, the Company recognized net income related to our equity method investments of $0.4 million.