The table below provides the amortized cost, unrealized gains and losses and fair values of debt securities summarized by major category (dollars in thousands):

The amortized cost and fair value of debt securities, by contractual maturity or pre-refunded date, are shown below. Mortgages underlying mortgage-backed securities may be called or prepaid; therefore, actual maturities could differ from the contractual maturities. All mortgage-backed securities were issued by U.S. government corporations and agencies (dollars in thousands).

Realized gains and losses related to sales and calls of debt securities available for sale are summarized as follows (dollars in thousands):

(1)

Net gains (losses) on sales of securities reported on the unaudited Consolidated Statements of Income includes sale of equity securities, excluded in this table.

Debt securities with carrying amounts of $591.7 million and $704.4 million on September 30, 2020 and December 31, 2019, respectively, were pledged as collateral for public deposits, securities sold under agreements to repurchase and for other purposes as required or permitted by law.

The following information pertains to debt securities with gross unrealized losses, aggregated by investment category and the length of time that individual securities have been in a continuous loss position (dollars in thousands):


	Less than 12 months, gross				12 months or more, gross				Total, gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
September 30, 2020:	Value		Losses		Value		Losses		Value		Losses
Debt securities available for sale
U.S. Treasury securities	$	—	$	—	$	—	$	—	$	—	$	—
Obligations of U.S. government corporations and agencies		—		—		5,479		(55)		5,479		(55)
Obligations of states and political subdivisions		3,810		(9)		—		—		3,810		(9)
Commercial mortgage-backed securities		53,690		(104)		—		—		53,690		(104)
Residential mortgage-backed securities		152,298		(301)		838		(3)		153,136		(304)
Corporate debt securities		7,563		(4)		—		—		7,563		(4)
Total temporarily impaired securities	$	217,361	$	(418)	$	6,317	$	(58)	$	223,678	$	(476)


	Less than 12 months, gross				12 months or more, gross				Total, gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
December 31, 2019:	Value		Losses		Value		Losses		Value		Losses
Debt securities available for sale
U.S. Treasury securities	$	—	$	—	$	—	$	—	$	—	$	—
Obligations of U.S. government corporations and agencies		6,362		(48)		—		—		6,362		(48)
Obligations of states and political subdivisions⁽¹⁾		4,981		(11)		1,548		—		6,529		(11)
Commercial mortgage-backed securities		33,322		(144)		2,044		(2)		35,366		(146)
Residential mortgage-backed securities		78,326		(245)		50,259		(379)		128,585		(624)
Corporate debt securities		—		—		—		—		—		—
Total temporarily impaired securities	$	122,991	$	(448)	$	53,851	$	(381)	$	176,842	$	(829)

(1)

Unrealized losses for 12 months or more, gross, was less than one thousand dollars.

Debt securities available for sale are not within the scope of CECL, however, the accounting for credit losses on these securities is affected by ASC 326-30. As of September 30, 2020, the Company’s debt security portfolio consisted of 1,190 securities. The total number of debt securities in the investment portfolio in an unrealized loss position as of September 30, 2020 was 37 and represented an unrealized loss of 0.21% of the aggregate fair value. The unrealized losses relate to changes in market interest rates and market conditions that do not represent credit-related impairments. Furthermore, the Company does not intend to sell such securities and it is more likely than not that the Company will recover the amortized cost prior to being required to sell the debt securities. Full collection of the amounts due according to the contractual terms of the debt securities is expected; therefore, the impairment related to noncredit factors is recognized in accumulated other comprehensive income (loss), net of applicable taxes, at September 30, 2020. As of September 30, 2020, the Company did not hold general obligation bonds of any single issuer, the aggregate of which exceeded 10% of the Company’s stockholders’ equity.