

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Available for sale at March 31, 2020
U.S. Treasury	$	596	$	4	$	—	$	600
U.S. Government-sponsored agency securities	12,398		80		—		12,478
State and municipal	898,991		50,523		306		949,208
U.S. Government-sponsored mortgage-backed securities	820,263		33,296		101		853,458
Corporate obligations	31		—		—		31
Total available for sale	1,732,279		83,903		407		1,815,775
Held to maturity at March 31, 2020
U.S. Government-sponsored agency securities	35,050		8		—		35,058
State and municipal	358,479		18,030		28		376,481
U.S. Government-sponsored mortgage-backed securities	487,150		19,989		—		507,139
Foreign investment	1,500		—		—		1,500
Total held to maturity	882,179		38,027		28		920,178
Total Investment Securities	$	2,614,458	$	121,930	$	435	$	2,735,953



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Available for sale at December 31, 2019
U.S. Government-sponsored agency securities	$	38,529	$	346	$	—	$	38,875
State and municipal	859,511		41,092		807		899,796
U.S. Government-sponsored mortgage-backed securities	842,349		10,378		1,404		851,323
Corporate obligations	31		—		—		31
Total available for sale	1,740,420		51,816		2,211		1,790,025
Held to maturity at December 31, 2019
U.S. Government-sponsored agency securities	15,619		1		37		15,583
State and municipal	354,115		15,151		107		369,159
U.S. Government-sponsored mortgage-backed securities	434,804		6,921		401		441,324
Foreign investment	1,500		—		—		1,500
Total held to maturity	806,038		22,073		545		827,566
Total Investment Securities	$	2,546,458	$	73,889	$	2,756	$	2,617,591

The increase in unrealized gains from December 31, 2019 to March 31, 2020 is primarily due to interest rate declines. The longer term points on the yield curve have declined since year-end which increases the fair value of securities in the portfolio.

The amortized cost and fair value of available for sale and held to maturity securities at March 31, 2020 and December 31, 2019, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties.



	Available for Sale				Held to Maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Maturity Distribution at March 31,2020:
Due in one year or less	$	1,945	$	1,965	$	8,740	$	8,762
Due after one through five years	4,800		4,932		33,393		33,947
Due after five through ten years	47,807		49,833		107,482		111,986
Due after ten years	857,464		905,587		245,414		258,344
	912,016		962,317		395,029		413,039
U.S. Government-sponsored mortgage-backed securities	820,263		853,458		487,150		507,139
Total Investment Securities	$	1,732,279	$	1,815,775	$	882,179	$	920,178



	Available for Sale				Held to Maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Maturity Distribution at December 31, 2019
Due in one year or less	$	1,134	$	1,136	$	9,920	$	10,105
Due after one through five years	5,031		5,141		45,197		45,654
Due after five through ten years	74,745		76,920		84,153		88,844
Due after ten years	817,161		855,505		231,964		241,639
	898,071		938,702		371,234		386,242
U.S. Government-sponsored mortgage-backed securities	842,349		851,323		434,804		441,324
Total Investment Securities	$	1,740,420	$	1,790,025	$	806,038	$	827,566

The following tables show the Corporation’s gross unrealized losses and fair value, aggregated by investment category and length of time the individual securities have been in a continuous unrealized loss position at March 31, 2020, and December 31, 2019:



	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Temporarily Impaired Available for Sale Securities at March 31, 2020
State and municipal	$	34,304	$	306	$	—	$	—	$	34,304	$	306
U.S. Government-sponsored mortgage-backed securities	17,011		101		—		—		17,011		101
Total Temporarily Impaired Available for Sale Securities	51,315		407		—		—		51,315		407
Temporarily Impaired Held to Maturity Securities at March 31,2020
State and municipal	6,815		28		—		—		6,815		28
Total Temporarily Impaired Held to Maturity Securities	6,815		28		—		—		6,815		28
Total Temporarily Impaired Investment Securities	$	58,130	$	435	$	—	$	—	$	58,130	$	435



	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Temporarily Impaired Available for Sale Securities at December 31, 2019
State and municipal	$	76,273	$	807	$	—	$	—	$	76,273	$	807
U.S. Government-sponsored mortgage-backed securities	127,673		1,326		20,796		78		148,469		1,404
Total Temporarily Impaired Available for Sale Securities	203,946		2,133		20,796		78		224,742		2,211
Temporarily Impaired Held to Maturity Securities at December 31, 2019
U.S. Government-sponsored agency securities	3,016		4		12,467		33		15,483		37
State and municipal	22,947		107		—		—		22,947		107
U.S. Government-sponsored mortgage-backed securities	124,253		364		7,991		37		132,244		401
Total Temporarily Impaired Held to Maturity Securities	150,216		475		20,458		70		170,674		545
Total Temporarily Impaired Investment Securities	$	354,162	$	2,608	$	41,254	$	148	$	395,416	$	2,756



	March 31, 2020			December 31, 2019
Investments reported at less than historical cost:
Historical cost	$	58,565		$	398,172
Fair value	58,130			395,416
Gross unrealized losses	$	435		$	2,756
Percent of the Corporation's investment portfolio	2.2		%	15.2		%

The Corporation's management believes the decline in fair value for these securities was temporary. Should the impairment of any of these securities become other-than-temporary, the cost basis of the investment will be reduced and the resulting loss recognized in net income during the period the other-than-temporary-impairment ("OTTI") is identified. The Corporation’s management has evaluated all securities with unrealized losses for OTTI and concluded no OTTI existed at March 31, 2020.

In determining the fair value of the investment securities portfolio, the Corporation utilizes a third party for portfolio accounting services, including market value input, for those securities classified as Level 1 and Level 2 in the fair value hierarchy. The Corporation has obtained an understanding of what inputs are being used by the vendor in pricing the portfolio and how the vendor classified these securities based upon these inputs. From these discussions, the Corporation’s management is comfortable that the classifications are proper. The Corporation has gained trust in the data for two reasons: (a) independent spot testing of the data is conducted by the Corporation through obtaining market quotes from various brokers on a periodic basis; and (b) actual gains or loss resulting from the sale of certain securities has proven the data to be accurate over time. Fair value of securities classified as Level 3 in the valuation hierarchy was determined using a discounted cash flow model that incorporated market estimates of interest rates and volatility in markets that have not been active.

The unrealized losses on the Corporation's investments in securities of state and political subdivisions were caused by interest rate changes. The contractual terms of those investments do not permit the issuer to settle the securities at a price less than the amortized cost basis of the investments. Because the Corporation does not intend to sell the investments and it is not more likely than not that the Corporation will be required to sell the investments before recovery of their amortized cost basis, which may be maturity, the Corporation does not consider those investments to be other-than-temporarily impaired at March 31, 2020. The state and municipal securities portfolio contains unrealized losses of $306,000 on seventeen securities and $28,000 on four securities in the available for sale and held to maturity portfolios, respectively. At March 31, 2020, the Corporation had little to no exposure to municipal bonds related to entertainment receipts, student housing, parking facilities, airports, nursing homes or public transit.

The unrealized losses on the Corporation's investment in mortgage-backed securities were a result of interest rate changes. The Corporation expects to recover the amortized cost basis over the term of the securities. Because the decline in market value is attributable to changes in interest rates and not credit quality, and because the Corporation does not intend to sell the investments and it is not more likely than not that the Corporation will be required to sell the investments before recovery of their amortized cost basis, which may be maturity, the Corporation does not consider those investments to be other-than-temporarily impaired at March 31, 2020. The mortgage-backed securities portfolio contains unrealized losses of $101,000 on three securities in the available for sale portfolio and no unrealized losses in the held to maturity portfolio. All these securities are issued by a U.S. government-sponsored entity and have an implicit or explicit government guarantee. The slowing of prepayments and the forbearance programs resulting from the financial impacts of COVID-19 could increase bond duration and potentially improve market values on these securities.