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, 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)	$	607,150	$	187	$	44,247	$	—	$	563,090
Fannie Mae (FNMA) mortgage-backed securities (MBS)	4,921,188		2,549		336,759		—		4,586,978
Freddie Mac (FHLMC) MBS	128,918		871		3,383		—		126,406
Ginnie Mae (GNMA) MBS	16,356		99		396		—		16,059
Government-sponsored enterprises (GSE) agency notes	229,938		—		26,542		—		203,396
	$	5,903,550	$	3,706	$	411,327	$	—	$	5,495,929
Held-to-Maturity Debt Securities(1)
State and political subdivisions	$	84,102	$	875	$	18	$	4	$	84,955
Foreign bonds	800		—		1		—		799
	$	84,902	$	875	$	19	$	4	$	85,754

(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 gains of $0.2 million at March 31, 2022, which are offset in Accumulated other comprehensive (loss) income. 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. 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, 2022 and December 31, 2021 are presented in the table below:


	Available-for-Sale
	Amortized		Fair
(Dollars in thousands)	Cost		Value
March 31, 2022 (1)
Within one year	$	2,744	$	2,744
After one year but within five years	104,877		103,153
After five years but within ten years	241,045		224,031
After ten years	5,554,884		5,166,001
	$	5,903,550	$	5,495,929
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 March 31, 2022, the Company’s available for sale investment securities consisted of 1,089 securities, 934 of which were in an unrealized loss position.

As of March 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 March 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.

The scheduled maturities of held-to-maturity debt securities at March 31, 2022 and December 31, 2021 are presented in the table below:


	Held-to-Maturity
	Amortized		Fair
(Dollars in thousands)	Cost		Value
March 31, 2022 (1)
Within one year	$	1,031	$	1,031
After one year but within five years	2,674		2,689
After five years but within ten years	38,696		39,217
After ten years	42,501		42,817
	$	84,902	$	85,754
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 5.5 years at March 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.

Investment securities with fair market values aggregating $2.7 billion and $2.2 billion were pledged as collateral for retail customer repurchase agreements, municipal deposits, and other obligations as of March 31, 2022 and December 31, 2021, respectively.

During the three months ended March 31, 2022, the Company had no sales of debt securities categorized as available-for-sale, resulting in no realized gains and no realized losses. During the three months ended March 31, 2021, the Company sold $9.3 million of debt securities categorized as available-for-sale resulting in $0.3 million of realized gains and no realized losses.

As of March 31, 2022 and December 31, 2021, the Company's debt securities portfolio had remaining unamortized premiums of $66.9 million and $69.4 million, respectively, and unaccreted discounts of $18.0 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 March 31, 2022.


	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	$	356,589	$	19,874	$	177,496	$	24,373	$	534,085	$	44,247
FNMA MBS	3,765,435		264,082		652,705		72,677		4,418,140		336,759
FHLMC MBS	70,215		2,064		9,168		1,319		79,383		3,383
GNMA MBS	8,377		212		2,023		184		10,400		396
GSE agency notes	38,880		4,178		164,516		22,364		203,396		26,542
	$	4,239,496	$	290,410	$	1,005,908	$	120,917	$	5,245,404	$	411,327

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, 2021.


	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 March 31, 2022, available-for-sale debt securities for which the amortized cost basis exceeded fair value totaled $5.2 billion. Total unrealized losses on these securities were $411.3 million at March 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 March 31, 2022.

At March 31, 2022 and December 31, 2021, held-to-maturity debt securities had an amortized cost basis of $84.9 million and $90.6 million, respectively. The held-to-maturity debt security portfolio primarily consists of 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, 2022, aggregated by credit quality indicator:


(Dollars in thousands)	State and political subdivisions		Foreign bonds
A+ rated or higher	$	84,102	$	800
Not rated	—		—
Ending balance	$	84,102	$	800

The following table summarizes the amortized cost of debt securities held-to-maturity as of December 31, 2021, aggregated by credit quality indicator:


(Dollars in thousands)	State and political subdivisions		Foreign bonds
A+ rated or higher	$	90,146	$	500
Not rated	—		—
Ending balance	$	90,146	$	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 foreign bond debt securities for the three months ended March 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 three months ended March 31, 2022 and 2021:


	Three months ended March 31,
(Dollars in thousands)	2022		2021
Allowance for credit losses:
Beginning balance	$	4	$	6

Provision for credit losses	—		(1)

Charge-offs, net	—		—

Ending balance	$	4	$	5

Accrued interest receivable of $0.7 million and $0.9 million as of March 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 March 31, 2022 and December 31, 2021.

During the three months ended March 31, 2022, total net loss on equity investments of $3 thousand was recorded driven by an unrealized loss on Visa Shares presented within Unrealized (loss) gain on equity investment, net in the Consolidated Statements of Income.