The following table summarizes the amortized cost and fair value of the available for sale investment securities portfolio at March 31, 2021 and December 31, 2020 and the corresponding amounts of unrealized gains and losses recognized in accumulated other comprehensive income:

			Gross		Gross
	Amortized		Unrealized		Unrealized
(In Thousands of Dollars)	Cost		Gains		Losses			Fair Value
March 31, 2021
U.S. Treasury and U.S. government sponsored entities	$	17,356	$	79	$	(370	)	$	17,065
State and political subdivisions		447,203		15,903		(2,689	)		460,417
Corporate bonds		3,679		92		(34	)		3,737
Mortgage-backed securities - residential		301,457		3,366		(4,301	)		300,522
Collateralized mortgage obligations - residential		15,499		440		(4	)		15,935
Small Business Administration		5,100		90		0			5,190
Totals	$	790,294	$	19,970	$	(7,398	)	$	802,866

			Gross		Gross
	Amortized		Unrealized		Unrealized
(In Thousands of Dollars)	Cost		Gains		Losses			Fair Value
December 31, 2020
U.S. Treasury and U.S. government sponsored entities	$	11,798	$	101	$	(54	)	$	11,845
State and political subdivisions		344,160		22,350		(204	)		366,306
Corporate bonds		3,582		132		(2	)		3,712
Mortgage-backed securities - residential		157,106		4,919		(243	)		161,782
Collateralized mortgage obligations - residential		25,654		742		(3	)		26,393
Small Business Administration		5,411		151		0			5,562
Totals	$	547,711	$	28,395	$	(506	)	$	575,600

Proceeds from the sale of portfolio securities were $26.2 million during the three month period ended March 31, 2021. Gross gains of $406.0 thousand along with gross losses of $22.6 thousand were realized on these sales during the three month period ended March 31, 2021. $105 thousand of realized gains during the three month period were recognized in the income statement for equity securities as of March 31, 2021. Proceeds from the sale of portfolio securities were $15.1 million during the three month period ended March 31, 2020. Gross gains were $256 thousand along with gross losses of $0 during the same three month ended March 31, 2020. $99 thousand of realized losses during the three month period ended March 31, 2020 were recognized in the income statement for equity securities.

The amortized cost and fair value of the debt securities portfolio are shown by expected maturity. Expected maturities may differ from contractual maturities if issuers have the right to call or prepay obligations with or without call or prepayment penalties. Securities not due at a single maturity date are shown separately.

	March 31, 2021
(In Thousands of Dollars)	Amortized Cost		Fair Value
Maturity
Within one year	$	3,006	$	3,044
One to five years		5,430		5,685
Five to ten years		44,780		46,080
Beyond ten years		415,022		426,410
Mortgage-backed, collateralized mortgage obligations and Small Business Administration securities		322,056		321,647
Total	$	790,294	$	802,866

The following table summarizes the available for sale investment securities with unrealized losses at March 31, 2021 and December 31, 2020, aggregated by major security type and length of time in a continuous unrealized loss position.

	Less than 12 Months					12 Months or Longer				Total
	Fair		Unrealized			Fair		Unrealized		Fair		Unrealized
(In Thousands of Dollars)	Value		Loss			Value		Loss		Value		Loss
March 31, 2021
U.S. Treasury and U.S. government sponsored entities	$	13,845	$	(370	)	$	0	$	0	$	13,845	$	(370	)
State and political subdivisions		84,208		(2,689	)		0		0		84,208		(2,689	)
Corporate bonds		714		(34	)		0		0		714		(34	)
Mortgage-backed securities - residential		153,691		(4,301	)		0		0		153,691		(4,301	)
Collateralized mortgage obligations - residential		277		(4	)		0		0		277		(4	)
Total	$	252,735	$	(7,398	)	$	0	$	0	$	252,735	$	(7,398	)

	Less than 12 Months					12 Months or Longer				Total
	Fair		Unrealized			Fair		Unrealized		Fair		Unrealized
(In Thousands of Dollars)	Value		Loss			Value		Loss		Value		Loss
December 31, 2020
U.S. Treasury and U.S. government sponsored entities	$	8,153	$	(54	)	$	0	$	0	$	8,153	$	(54	)
State and political subdivisions		19,205		(204	)		0		0		19,205		(204	)
Corporate bonds		198		(2	)		0		0		198		(2	)
Mortgage-backed securities - residential		63,401		(243	)		0		0		63,401		(243	)
Collateralized mortgage obligations - residential		294		(3	)		0		0		294		(3	)
Total	$	91,251	$	(506	)	$	0	$	0	$	91,251	$	(506	)

The Company has adopted ASU 2016-13 that makes improvements to the accounting for credit losses on securities available for sale. The concept of other than-temporarily impaired securities has been replaced with the allowance for credit losses. Securities available for sale are evaluated on an individual level and pooling of securities is no longer an option. During this evaluation process, management considers the extent to which the fair value has been less than cost, the financial condition and near term prospects of the issuer, and the intent and ability of the Company to hold the security for a period of time sufficient to allow for any anticipated recovery in fair value.

If the Company determines that a credit loss exists, the credit portion of the allowance will be measured using a discounted cash flow analysis using the effective interest rate as of the security’s purchase date. As of March 31, 2021, the Company’s security portfolio consisted of 767 securities, 153 of which were in an unrealized loss position. The majority of the unrealized losses on the Company’s securities are related to its holdings of state and political subdivisions and mortgage-backed securities. The Company does not consider its AFS securities with unrealized losses to be attributable to credit-related factors, as the unrealized losses have occurred as a result of changes in noncredit related factors such as changes in interest rates, market spreads and market conditions subsequent to purchase, not credit deterioration. As of March 31, 2021 no allowance for credit losses on AFS securities was recorded.