There were no sales of investment securities during the six months ended June 30, 2019 and 2018. Investment securities with an aggregate carrying value of $569,296,000 and $597,591,000 at June 30, 2019 and December 31, 2018, respectively, were pledged as collateral for specific borrowings, lines of credit or local agency deposits.

The amortized cost and estimated fair value of debt securities at June 30, 2019 by contractual maturity are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. At June 30, 2019, obligations of U.S. government corporations and agencies with a cost basis totaling $1,026,710,000 consist almost entirely of residential real estate mortgage-backed securities whose contractual maturity, or principal repayment, will follow the repayment of the underlying mortgages. For purposes of the following table, the entire outstanding balance of these mortgage-backed securities issued by U.S. government corporations and agencies is categorized based on final maturity date. At June 30, 2019, the Company estimates the average remaining life of these mortgage-backed securities issued by U.S. government corporations and agencies to be approximately 5.1 years. Average remaining life is defined as the time span after which the principal balance has been reduced by half.


Debt Securities	Available for Sale				Held to Maturity
(In thousands)	Amortized		Estimated		Amortized		Estimated
(In thousands)	Cost		Fair Value		Cost		Fair Value
Due in one year	$	2,415	$	2,421	$	—	$	—
Due after one year through five years		14,287		14,636		1,254		1,269
Due after five years through ten years		44,325		45,235		21,922		22,166
Due after ten years		1,071,678		1,071,702		389,348		391,841

Totals	$	1,132,705	$	1,133,994	$	412,524	$	415,276

Gross unrealized losses on debt securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, were as follows:


	Less than 12 months					12 months or more					Total
	Fair		Unrealized			Fair		Unrealized			Fair		Unrealized
	Value		Loss			Value		Loss			Value		Loss
	(in thousands)
June 30, 2019
Debt Securities Available for Sale
Obligations of U.S. government agencies	$	—	$	—		$	247,286	$	(2,278	)	$	247,286	$	(2,278	)
Obligations of states and political subdivisions		5,208		(108	)		—		—			5,208		(108	)
Corporate Bonds		—		—			—		—			—		—
Asset backed securities		340,012		(4,346	)		—		—			340,012		(4,346	)
Total debt securities available for sale	$	345,220	$	(4,454	)	$	247,286	$	(2,278	)	$	592,506	$	(6,732	)
Debt Securities Held to Maturity
Obligations of U.S. government agencies	$	—	$	—		$	110,702	$	(1,199	)	$	110,702	$	(1,199	)
Obligations of states and political subdivisions		—		—			—		—			—		—
Total debt securities held to maturity	$	—	$	—		$	110,702	$	(1,199	)	$	110,702	$	(1,199	)

	Less than 12 months					12 months or more					Total
	Fair		Unrealized			Fair		Unrealized			Fair		Unrealized
	Value		Loss			Value		Loss			Value		Loss
	(in thousands)
December 31, 2018
Debt Securities Available for Sale
Obligations of U.S. government agencies	$	171,309	$	(3,588	)	$	394,630	$	(14,490	)	$	565,939	$	(18,078	)
Obligations of states and political subdivisions		63,738		(1,541	)		20,719		(1,571	)		84,457		(3,112	)
Asset backed securities		101,386		(1,019	)		—		—			101,386		(1,019	)
Total debt securities available for sale	$	336,433	$	(6,148	)	$	415,349	$	(16,061	)	$	751,782	$	(22,209	)
Debt Securities Held to Maturity
Obligations of U.S. government agencies	$	223,810	$	(2,619	)	$	158,648	$	(5,126	)	$	382,458	$	(7,745	)
Obligations of states and political subdivisions		5,786		(114	)		4,042		(116	)		9,828		(230	)
Total debt securities held to maturity	$	229,596	$	(2,733	)	$	162,690	$	(5,242	)	$	392,286	$	(7,975	)

Obligations of U.S. government agencies: Unrealized losses on investments in obligations of U.S. government agencies are caused by interest rate increases. The contractual cash flows of these securities are guaranteed by U.S. Government Sponsored Entities (principally Fannie Mae and Freddie Mac). It is expected that the securities would not be settled at a price less than the amortized cost of the investment. Because the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, these investments are not considered other-than-temporarily impaired. At June 30, 2019, 46 debt securities representing obligations of U.S. government agencies had unrealized losses with aggregate depreciation of (1.0%) from the Company’s amortized cost basis.

Obligations of states and political subdivisions: The unrealized losses on investments in obligations of states and political subdivisions were caused by increases in required yields by investors in these types of securities. It is expected that the securities would not be settled at a price less than the amortized cost of the investment. Because the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, these investments are not considered other-than-temporarily impaired. At June 30, 2019, 13 debt securities representing obligations of states and political subdivisions had unrealized losses with aggregate depreciation of (2.0%) from the Company’s amortized cost basis.

Asset backed securities: The unrealized losses on investments in asset backed securities were caused by increases in required yields by investors in these types of securities. At the time of purchase, each of these securities was rated AA or AAA and through June 30, 2019 has not experienced any deterioration in credit rating. The Company continues to monitor these securities for changes in credit rating or other indications of credit deterioration. Because management believes the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Company does not intend to sell and more likely than not will not be required to sell, these investments are not considered other-than-temporarily impaired. At June 30, 2019, 28 asset backed securities had unrealized losses with aggregate depreciation of (1.3%) from the Company’s amortized cost basis.

Marketable equity securities: All unrealized losses recognized during the reporting period were for equity securities still held at June 30, 2019.