Investment securities are classified as available for sale, held to maturity, or equity on the consolidated balance sheets at the time of purchase. The amortized cost and fair values of securities available for sale and held to maturity at March 31, 2020 were as follows:


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


Investment securities available for sale

U.S. government SBA agency securities	$	10,241	$	2	$	(5)	$	10,238
Obligations of state and political subdivisions (municipal securities)	492,195		16,443		(1)		508,636
Residential mortgage-related securities
FNMA / FHLMC	103,576		908		—		104,485
GNMA	799,983		23,804		—		823,787

Commercial mortgage-related securities
FNMA / FHLMC	19,861		2,912		—		22,773
GNMA	1,108,336		10,162		(4,055)		1,114,443
FFELP asset backed securities	360,658		—		(19,234)		341,424

Other debt securities	3,000		—		—		3,000
Total investment securities available for sale	$	2,897,851	$	54,231	$	(23,295)	$	2,928,787
Investment securities held to maturity
U. S. Treasury securities	$	999	$	42	$	—	$	1,041
Obligations of state and political subdivisions (municipal securities)	1,426,543		82,382		(475)		1,508,451
Residential mortgage-related securities
FNMA / FHLMC	78,125		3,486		—		81,610
GNMA	245,675		8,124		—		253,799
GNMA commercial mortgage-related securities	398,092		6,500		(1,939)		402,653
Total investment securities held to maturity	$	2,149,434	$	100,534	$	(2,414)	$	2,247,553


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


Investment securities available for sale

Obligations of state and political subdivisions (municipal securities)	$	529,908	$	16,269	$	(18)	$	546,160
Residential mortgage-related securities
FNMA / FHLMC	131,158		1,562		(59)		132,660
GNMA	982,941		3,887		(1,689)		985,139

Commercial mortgage-related securities
FNMA / FHLMC	19,929		1,799		—		21,728
GNMA	1,314,836		7,403		(12,032)		1,310,207
FFELP asset backed securities	270,178		—		(6,485)		263,693

Other debt securities	3,000		—		—		3,000
Total investment securities available for sale	$	3,251,950	$	30,920	$	(20,284)	$	3,262,586
Investment securities held to maturity
U. S. Treasury securities	$	999	$	19	$	—	$	1,018
Obligations of state and political subdivisions (municipal securities)	1,418,569		69,775		(1,118)		1,487,227
Residential mortgage-related securities
FNMA / FHLMC	81,676		1,759		(15)		83,420
GNMA	269,523		1,882		(1,108)		270,296
GNMA commercial mortgage-related securities	434,317		6,308		(6,122)		434,503
Total investment securities held to maturity	$	2,205,083	$	79,744	$	(8,363)	$	2,276,465

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 available for sale and held to maturity at March 31, 2020 are shown below:


	Available for Sale							Held to Maturity
($ in Thousands)	Amortized Cost		Fair Value			Amortized Cost		Fair Value
Due in one year or less	$	10,731	$	10,738		$	32,555	$	32,703
Due after one year through five years	30,829		31,242			77,586		78,683
Due after five years through ten years	324,501		334,499			153,519		158,843
Due after ten years	129,134		135,157			1,163,883		1,239,262
Total debt securities	495,195		511,636			1,427,542		1,509,492
U.S. government SBA agency securities	10,241		10,238			—		—
Residential mortgage-related securities
FNMA / FHLMC	103,576		104,485			78,125		81,610
GNMA	799,983		823,787			245,675		253,799

Commercial mortgage-related securities
FNMA / FHLMC	19,861		22,773			—		—
GNMA	1,108,336		1,114,443			398,092		402,653
FFELP asset backed securities	360,658		341,424			—		—

Total investment securities	$	2,897,851	$	2,928,787		$	2,149,434	$	2,247,553
Ratio of fair value to amortized cost			101.1		%			104.6		%


($ in Thousands)	AAA		AA		A		Total
U. S. Treasury securities	$	999	$	—	$	—	$	999
Obligations of state and political subdivisions (municipal securities)	543,620		862,040		20,883		1,426,543
Residential mortgage-related securities
FNMA/FHLMC	78,125		—		—		78,125
GNMA	245,675		—		—		245,675
GNMA commercial mortgage-related securities	398,092		—		—		398,092
Total held to maturity securities	$	1,266,510	$	862,040	$	20,883	$	2,149,434

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 months ended March 31, 2020 and 2019 are shown below:


	Three Months Ended March 31,
($ in Thousands)	2020		2019
Gross gains on available for sale securities	$	6,198	$	1,680
Gross gains on held to maturity securities	—		—
Total gains	6,198		1,680
Gross (losses) on available for sale securities	(80)		—
Gross (losses) on held to maturity securities	—		—
Total (losses)	(80)		—

Investment securities gains (losses), net	$	6,118	$	1,680
Proceeds from sales of investment securities	$	365,239	$	131,122

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.

At March 31, 2020, accrued interest receivable on held to maturity and available for sale securities totaled $14 million and $10 million, respectively, both which are included in interest receivable on the consolidated balance sheets. There was no interest income reversed for investments going into nonaccrual.

The allowance for credit losses on held to maturity securities was approximately $61,000 at March 31, 2020, attributable entirely to the Corporation's municipal securities, included in investment securities held to maturity, net, at amortized cost on the consolidated balance sheets. The Corporation also holds U.S. Treasury and residential 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 available for sale and held to maturity, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position, at March 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 available for sale

U.S. government SBA agency securities	7	$	(5)	$	4,958	—	$	—	$	—	$	(5)	$	4,958
Obligations of state and political subdivisions (municipal securities)	5	(1)		1,313		—	—		—		(1)		1,313




GNMA commercial mortgage-related securities	22	(1,111)		259,273		8	(2,944)		138,611		(4,055)		397,883
FFELP asset backed securities	16	(10,971)		222,197		10	(8,262)		119,228		(19,234)		341,424
Other debt securities	2	—		2,000		—	—		—		—		2,000

Total	52	$	(12,089)	$	489,740	18	$	(11,206)	$	257,838	$	(23,295)	$	747,578
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	22	$	(470)	$	28,779	3	$	(5)	$	542	$	(475)	$	29,321
Residential mortgage-related securities
FNMA / FHLMC	1	—		—		—	—		—		—		—

GNMA commercial mortgage-related securities	8	(332)		126,170		7	(1,607)		126,624		(1,939)		252,794
Total	31	$	(802)	$	154,950	10	$	(1,612)	$	127,166	$	(2,414)	$	282,116

For comparative purposes, the following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2019:


	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 available for sale

Obligations of state and political subdivisions (municipal securities)	4	$	(18)	$	1,225	—	$	—	$	—	$	(18)	$	1,225
Residential mortgage-related securities
FNMA / FHLMC	—	—		—		4	(59)		34,807		(59)		34,807
GNMA	18	(924)		322,394		3	(766)		79,461		(1,689)		401,856

GNMA commercial mortgage-related securities	22	(810)		258,218		42	(11,222)		621,307		(12,032)		879,524
FFELP asset backed securities	19	(6,092)		250,780		2	(393)		12,913		(6,485)		263,693
Other debt securities	2	—		2,000		—	—		—		—		2,000

Total	65	$	(7,843)	$	834,616	51	$	(12,440)	$	748,487	$	(20,284)	$	1,583,104
Investment securities held to maturity
Obligations of state and political subdivisions (municipal securities)	52	$	(1,105)	$	77,562	6	$	(13)	$	2,378	$	(1,118)	$	79,940
Residential mortgage-related securities
FNMA / FHLMC	1	(6)		1,242		1	(9)		833		(15)		2,075
GNMA	12	(1,059)		187,261		8	(49)		6,587		(1,108)		193,849
GNMA commercial mortgage-related securities	2	(29)		26,202		21	(6,093)		357,733		(6,122)		383,935
Total	67	$	(2,199)	$	292,267	36	$	(6,164)	$	367,532	$	(8,363)	$	659,799

The Corporation reviews the available for sale 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 the impairment analysis includes the extent to which the security has been in an unrealized loss position, the change in security rating, financial condition and near-term prospects of the issuer, as well as the security and industry specific economic conditions.

Based on the Corporation’s evaluation, management does not believe any available for sale securities in an unrealized loss position at March 31, 2020 represent credit deterioration as these unrealized losses are primarily attributable to changes in interest rates and the current market conditions. The unrealized losses reported for municipal securities at March 31, 2020 pertain to various state and local political subdivisions and school districts, and have declined due to the decrease in overall

interest rates. The unrealized losses at March 31, 2020 for mortgage-related securities have also declined due to the decrease in overall interest rates. The U.S. Treasury 3 year and 5 year rates decreased by 133 bp and 132 bp, respectively, from December 31, 2019. 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. At March 31, 2020 and December 31, 2019, the Corporation had FHLB stock of $145 million and $149 million, respectively. The Corporation had Federal Reserve Bank stock of $78 million at both March 31, 2020 and December 31, 2019.

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. At both March 31, 2020 and December 31, 2019, the Corporation had equity securities with readily determinable fair values of $2 million.