The amortized cost and fair values of securities AFS and HTM at December 31, 2020 were as follows:


($ in Thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses)		Fair Value


Investment securities AFS
U. S. Treasury securities	$	26,436	$	95	$	—	$	26,531
Agency securities	24,985		53		—		25,038
Obligations of state and political subdivisions (municipal securities)	425,057		25,605		—		450,662
Residential mortgage-related securities
FNMA / FHLMC	1,448,806		12,935		(500)		1,461,241
GNMA	231,364		4,176		(3)		235,537

Commercial mortgage-related securities
FNMA / FHLMC	19,654		3,250		—		22,904
GNMA	511,429		13,327		—		524,756
Asset backed securities
FFELP	329,030		1,172		(3,013)		327,189
SBA	8,637		—		(53)		8,584
Other debt securities	3,000		—		—		3,000
Total investment securities AFS	$	3,028,399	$	60,612	$	(3,570)	$	3,085,441
Investment securities HTM
U. S. Treasury securities	$	999	$	25	$	—	$	1,024
Obligations of state and political subdivisions (municipal securities)	1,441,900		133,544		—		1,575,445
Residential mortgage-related securities
FNMA / FHLMC	54,599		2,891		—		57,490
GNMA	114,553		4,260		—		118,813
Commercial mortgage-related securities
FNMA / FHLMC	11,211		—		—		11,211
GNMA	255,742		9,218		—		264,960
Total investment securities HTM	$	1,879,005	$	149,938	$	—	$	2,028,943

Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. The expected maturities of investment securities AFS and HTM at September 30, 2021, are shown below:


	AFS					HTM
($ in Thousands)	Amortized Cost		Fair Value			Amortized Cost		Fair Value
Due in one year or less	$	7,987	$	7,996		$	27,797	$	27,982
Due after one year through five years	75,545		75,970			39,029		40,265
Due after five years through ten years	415,467		430,634			181,911		189,290
Due after ten years	37,565		41,396			1,293,705		1,387,099
Total debt securities	536,564		555,997			1,542,442		1,644,635
Residential mortgage-related securities
FNMA / FHLMC	2,377,335		2,377,408			37,318		39,447
GNMA	77,199		79,696			54,900		57,228
Private-label	76,033		76,033			—		—
Commercial mortgage-related securities
FNMA / FHLMC	357,837		353,175			170,739		166,985
GNMA	227,622		231,096			124,383		127,562
Asset backed securities
FFELP	212,378		212,797			—		—
SBA	7,182		7,179			—		—

Total investment securities	$	3,872,150	$	3,893,379		$	1,929,783	$	2,035,858
Ratio of fair value to amortized cost			100.5		%			105.5		%

On a quarterly basis, the Corporation refreshes the credit quality of each HTM security. The following table summarizes the credit quality indicators of HTM securities at amortized cost at September 30, 2021:


($ in Thousands)	AAA		AA		A		Not Rated		Total
U. S. Treasury securities	$	1,000	$	—	$	—	$	—	$	1,000
Obligations of state and political subdivisions (municipal securities)	683,098		847,641		10,511		194		1,541,443
Residential mortgage-related securities
FNMA / FHLMC	37,318		—		—		—		37,318
GNMA	54,900		—		—		—		54,900
Commercial mortgage-related securities
FNMA / FHLMC	170,739		—		—		—		170,739
GNMA	124,383		—		—		—		124,383
Total HTM securities	$	1,071,438	$	847,641	$	10,511	$	194	$	1,929,783

The following table summarizes the credit quality indicators of HTM securities at amortized cost at December 31, 2020:


($ in Thousands)	AAA		AA		A		Total
U. S. Treasury securities	$	999	$	—	$	—	$	999
Obligations of state and political subdivisions (municipal securities)	567,252		860,607		14,041		1,441,900
Residential mortgage-related securities
FNMA / FHLMC	54,599		—		—		54,599
GNMA	114,553		—		—		114,553
Commercial mortgage-related securities
FNMA / FHLMC	11,211		—		—		11,211
GNMA	255,742		—		—		255,742
Total HTM securities	$	1,004,357	$	860,607	$	14,041	$	1,879,005

Investment securities gains (losses), net includes proceeds from the sale of investment securities as well as any applicable write-ups or write-downs of investment securities. The proceeds from the sale of investment securities for the three and nine months ended September 30, 2021 and 2020, are shown below:


	Three Months Ended Sep 30,				Nine Months Ended Sep 30,
($ in Thousands)	2021		2020		2021		2020
Gross gains on AFS securities	$	—	$	7	$	421	$	9,312


Gross (losses) on AFS securities	—		—		(437)		(90)



Investment securities gains (losses), net	$	—	$	7	$	(16)	$	9,222
Proceeds from sales of investment securities	$	—	$	8	$	158,708	$	626,283

During the second quarter of 2021, the Corporation sold $107 million of lower yielding FFELP student loan asset backed securities at a slight gain and reinvested the proceeds into higher yielding mortgage backed securities. During the first quarter of 2021, the Corporation sold $51 million of lower yielding U.S. Treasury and Agency securities at a slight loss to take advantage of the steeper yield curve by reinvesting the proceeds into similar but higher yielding, longer duration securities.

During the second quarter of 2020, the Corporation sold $261 million of less liquid securities at a gain of $3 million, reinvesting the proceeds into more liquid securities in order to further improve portfolio liquidity. During the first quarter of 2020, the Corporation sold $281 million of primarily prepayment sensitive mortgage-related securities at a gain of $6 million. Additionally, in February 2020, the Corporation sold $84 million of certain securities acquired in the First Staunton acquisition that did not fit the parameters of the Corporation's current investment strategy.

Accrued interest receivable on HTM securities totaled $12 million and $14 million at September 30, 2021 and December 31, 2020, respectively. Accrued interest receivable on AFS securities totaled $9 million and $8 million at September 30, 2021 and December 31, 2020, respectively. Accrued interest receivable on both HTM and AFS securities is included in interest receivable on the consolidated balance sheets. There was no interest income reversed for investments going into nonaccrual at both September 30, 2021 and 2020.

The allowance for credit losses on HTM securities was approximately $49,000 at September 30, 2021 and approximately $67,000 at December 31, 2020, attributable entirely to the Corporation's municipal securities, included in investment securities HTM, net, at amortized cost on the consolidated balance sheets. The Corporation also holds U.S. Treasury, municipal and mortgage-related securities issued by the U.S. government or a GSE which are backed by the full faith and credit of the U.S. government and, as a result, no allowance for credit losses has been recorded related to these securities.

The following represents gross unrealized losses and the related fair value of investment securities AFS and HTM, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position, at September 30, 2021:


	Less than 12 months					12 months or more					Total
($ in Thousands)	Number of Securities	Unrealized (Losses)		Fair Value		Number of Securities	Unrealized (Losses)		Fair Value		Unrealized (Losses)		Fair Value
Investment securities AFS
U.S. Treasury securities	4	$	(319)	$	84,071	—	—		$	—	$	(319)	$	84,071
Agency securities	1	(2)		14,998		—	—		—		(2)		14,998

Residential mortgage-related securities
FNMA / FHLMC	33	(9,144)		1,170,981		—	—		—		(9,144)		1,170,981
GNMA	1	—		69		—	—		—		—		69


FNMA / FHLMC commercial mortgage-related securities	19	(6,892)		331,504		—	—		—		(6,892)		331,504

Asset backed securities
FFELP	1	(124)		34,876		8	(347)		65,002		(471)		99,878
SBA	—	—		—		9	(48)		4,229		(48)		4,229
Other debt securities	1	(1)		999		—	—		—		(1)		999

Total	60	$	(16,482)	$	1,637,498	17	$	(395)	$	69,231	$	(16,877)	$	1,706,729
Investment securities HTM
Obligations of state and political subdivisions (municipal securities)	62	$	(3,996)	$	151,216	—	$	—	$	—	$	(3,996)	$	151,216



Commercial mortgage-related securities
FNMA / FHLMC	11	(4,002)		146,248		—	—		—		(4,002)		146,248
GNMA	1	(22)		15,631		—	—		—		(22)		15,631
Total	74	$	(8,019)	$	313,096	—	$	—	$	—	$	(8,019)	$	313,096

For comparative purposes, the following represents gross unrealized losses and the related fair value of investment securities AFS and HTM, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2020:


	Less than 12 months					12 months or more					Total
($ in Thousands)	Number of Securities	Unrealized (Losses)		Fair Value		Number of Securities	Unrealized (Losses)		Fair Value		Unrealized (Losses)		Fair Value
Investment securities AFS


Residential mortgage-related securities
FNMA / FHLMC	7	$	(500)	$	163,002	—	$	—	$	—	$	(500)	$	163,002
GNMA	2	(3)		9,784		—	—		—		(3)		9,784

GNMA commercial mortgage-related securities	1	—		287		—	—		—		—		287
Asset backed securities
FFELP	1	(129)		9,267		16	(2,885)		178,681		(3,013)		187,948
SBA	14	(53)		8,379		—	—		—		(53)		8,379
Other debt securities	2	—		2,000		—	—		—		—		2,000

Total	27	$	(685)	$	192,720	16	$	(2,885)	$	178,681	$	(3,570)	$	371,400
Investment securities HTM



GNMA residential mortgage-related securities	1	$	—	$	325	—	$	—	$	—	$	—	$	325

Total	1	$	—	$	325	—	$	—	$	—	$	—	$	325

The Corporation reviews the AFS investment securities portfolio on a quarterly basis to monitor its credit exposure. A determination as to whether a security’s decline in fair value is the result of credit risk takes into consideration numerous factors and the relative significance of any single factor can vary by security. Some factors the Corporation may consider in this impairment analysis include the extent to which the security has been in an unrealized loss position, the change in security

Based on the Corporation’s evaluation, management does not believe any unrealized losses at September 30, 2021 represent credit deterioration as these unrealized losses are primarily attributable to changes in interest rates and the current market conditions. The U.S. Treasury 3 year and 5 year rates increased by 36 bp and 62 bp, respectively, from December 31, 2020. The Corporation does not intend to sell nor does it believe that it will be required to sell the securities in an unrealized loss position before recovery of their amortized cost basis.

FHLB and Federal Reserve Bank stocks: The Corporation is required to maintain Federal Reserve Bank stock and FHLB stock as a member of both the Federal Reserve System and the FHLB, and in amounts as required by these institutions. These equity securities are “restricted” in that they can only be sold back to the respective institutions or another member institution at par. Therefore, they are less liquid than other marketable equity securities and their fair value is equal to amortized cost. The Corporation had FHLB stock of $82 million at both September 30, 2021 and December 31, 2020. The Corporation had Federal Reserve Bank stock of $87 million at both September 30, 2021 and December 31, 2020. Accrued interest receivable on FHLB stock totaled approximately $974,000 and $972,000 at September 30, 2021 and December 31, 2020, respectively. There was $327,000 accrued interest receivable on Federal Reserve Bank stock at September 30, 2021 and none at December 31, 2020. Accrued interest receivable on both FHLB stock and Federal Reserve Bank stock is included in interest receivable on the consolidated balance sheets.

Equity securities with readily determinable fair values: The Corporation's portfolio of equity securities with readily determinable fair values is primarily comprised of CRA Qualified Investment mutual funds and a money market mutual fund. At September 30, 2021 and December 31, 2020, the Corporation had equity securities with readily determinable fair values of $4 million and $2 million, respectively.