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

(1)	Gross unrealized losses less than one thousand dollars.


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
December 31, 2018:	Cost		Gains		Losses		Value
Debt securities available for sale
U.S. Treasury securities	$	25,824	$	1	$	(414)	$	25,411
Obligations of U.S. government corporations and agencies		53,096		7		(761)		52,342
Obligations of states and political subdivisions		171,131		484		(1,571)		170,044
Commercial mortgage-backed securities		2,003		—		(61)		1,942
Residential mortgage-backed securities		322,646		245		(7,143)		315,748
Corporate debt securities		132,513		61		(376)		132,198
Total	$	707,213	$	798	$	(10,326)	$	697,685

Debt securities held to maturity
Obligations of states and political subdivisions	$	33,947	$	68	$	(87)	$	33,928
Commercial mortgage-backed securities		59,054		11		(1,003)		58,062
Residential mortgage-backed securities		515,659		1,748		(6,037)		511,370
Total	$	608,660	$	1,827	$	(7,127)	$	603,360

In adopting ASU 2017-12, the Company reassessed the classification of certain investments during the first quarter of 2019 and transferred $573.6 million of securities from held to maturity to available for sale. The transfer occurred at fair value and had a related unrealized loss of $4.8 million recorded in other comprehensive income.

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 agencies and corporations (dollars in thousands).


	Debt securities available for sale				Debt securities held to maturity
	Amortized		Fair		Amortized		Fair
June 30, 2019:	Cost		Value		Cost		Value
Due in one year or less	$	220,023	$	220,304	$	2,724	$	2,729
Due after one year through five years		418,649		424,241		11,861		12,035
Due after five years through ten years		263,388		267,989		1,123		1,170
Due after ten years		925,554		935,539		—		—
Total	$	1,827,614	$	1,848,073	$	15,708	$	15,934

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


	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Gross security gains	$	391	$	—	$	391	$	—
Gross security (losses)		(401)		—		(584)		—
Net (losses) gains on sales of securities⁽¹⁾	$	(10)	$	—	$	(193)	$	—

(1)

Net (losses) gains 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 $755.1 million and $498.3 million on June 30, 2019 and December 31, 2018, respectively, were pledged as collateral for public deposits, securities sold under agreements to repurchase and for other purposes as required or permitted by law.

Information pertaining to debt securities with gross unrealized losses aggregated by investment category and length of time that individual securities have been in a continuous loss position, follows (dollars in thousands):



	For less than				For greater
	12 months, gross				than 12 months, gross				Total, gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
June 30, 2019:	Value		Losses		Value		Losses		Value		Losses
Debt securities available for sale
U.S. Treasury securities	$	—	$	—	$	24,768	$	(33)	$	24,768	$	(33)
Obligations of U.S. government corporations and agencies⁽¹⁾		51		—		22,468		(48)		22,519		(48)
Obligations of states and political subdivisions		1,394		(8)		24,192		(46)		25,586		(54)
Commercial mortgage-backed securities		—		—		14,746		(33)		14,746		(33)
Residential mortgage-backed securities		13,629		(8)		183,552		(1,247)		197,181		(1,255)
Corporate debt securities		1,765		(7)		15,049		(10)		16,814		(17)
Total temporarily impaired securities	$	16,839	$	(23)	$	284,775	$	(1,417)	$	301,614	$	(1,440)

Debt securities held to maturity
Obligations of states and political subdivisions⁽¹⁾	$	—	$	—	$	500	$	—	$	500	$	—

(1)

Unrealized losses less than one thousand dollars.



	For less than				For greater
	12 months, gross				than 12 months, gross				Total, gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
December 31, 2018:	Value		Losses		Value		Losses		Value		Losses
Debt securities available for sale
U.S. Treasury securities	$	995	$	(4)	$	24,343	$	(410)	$	25,338	$	(414)
Obligations of U.S. government corporations and agencies		749		(3)		50,744		(758)		51,493		(761)
Obligations of states and political subdivisions		49,893		(460)		77,651		(1,111)		127,544		(1,571)
Commercial mortgage-backed securities		—		—		1,942		(61)		1,942		(61)
Residential mortgage-backed securities		48,387		(496)		247,573		(6,647)		295,960		(7,143)
Corporate debt securities		90,713		(268)		15,083		(108)		105,796		(376)
Total temporarily impaired securities	$	190,737	$	(1,231)	$	417,336	$	(9,095)	$	608,073	$	(10,326)

Debt securities held to maturity
Obligations of states and political subdivisions	$	9,531	$	(33)	$	9,538	$	(54)	$	19,069	$	(87)
Commercial mortgage-backed securities		12,067		(212)		45,041		(791)		57,108		(1,003)
Residential mortgage-backed securities		77,071		(974)		245,128		(5,063)		322,199		(6,037)
Total temporarily impaired securities	$	98,669	$	(1,219)	$	299,707	$	(5,908)	$	398,376	$	(7,127)

Debt securities are periodically evaluated for other-than-temporary impairment (“OTTI”). As of June 30, 2019, the Company’s debt security portfolio consisted of 1,273 securities. The total number of debt securities in the investment portfolio in an unrealized loss position as of June 30, 2019 was 126 and represented an unrealized loss of 0.47% of the aggregate amortized cost. 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 Company does not consider these investments to be OTTI at June 30, 2019. As of June 30, 2019, the Company did not hold general obligation bonds of any single issuer, the aggregate of which exceeded 10% of the Company’s stockholders’ equity.