Investment Securities

The amortized cost, gross unrealized gains and losses and estimated fair values for available-for-sale and held-to-maturity securities by major security type at March 31, 2020 and December 31, 2019 were as follows (in thousands):



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Fair Value
March 31, 2020
Available-for-sale:
U.S. Treasury securities and obligations of U.S. government corporations & agencies	$	56,067	$	716	$	(94	)	$	56,689
Obligations of states and political subdivisions	167,146		260		(3,904		)	163,502
Mortgage-backed securities: GSE residential	385,194		10,717		(400		)	395,511
Other securities	2,028		112		(41		)	2,099
Total available-for-sale	$	610,435	$	11,805	$	(4,439	)	$	617,801
Held-to-maturity:
U.S. Treasury securities and obligations of U.S. government corporations & agencies	$	24,563	$	243	$	—		$	24,806

December 31, 2019
Available-for-sale:
U.S. Treasury securities and obligations of U.S. government corporations & agencies	$	106,428	$	952	$	(60	)	$	107,320
Obligations of states and political subdivisions	172,460		5,990		(17		)	178,433
Mortgage-backed securities: GSE residential	391,307		5,331		(512		)	396,126
Other securities	4,028		141		—			4,169
Total available-for-sale	$	674,223	$	12,414	$	(589	)	$	686,048
Held-to-maturity:
U.S. Treasury securities and obligations of U.S. government corporations & agencies	$	69,542	$	99	$	(69	)	$	69,572

All of the Company's held-to-maturity securities are government agency-backed securities for which the risk of loss is minimal. As such, as of March 31, 2020, the Company did not recorded an allowance for credit losses on its held-to-maturity securities.

Realized gains and losses resulting from sales of securities were as follows during the three months ended March 31, 2020 and 2019 (in thousands):



	Three months ended March 31,
	2020		2019
Gross gains	$	531	$	84
Gross losses	—		(30		)

The following table indicates the expected maturities of investment securities classified as available-for-sale presented at fair value, and held-to-maturity presented at amortized cost, at March 31, 2020 and the weighted average yield for each range of maturities (dollars in thousands):



	One year or less			After 1 through 5 years			After 5 through 10 years			After ten years			Total
Available-for-sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	41,026		$	15,663		$	—		$	—		$	56,689
Obligations of state and political subdivisions	26,677			69,512			65,164			2,149			163,502
Mortgage-backed securities: GSE residential	73,878			310,186			11,447			—			395,511
Other securities	—			1,759			—			340			2,099
Total available-for-sale investments	$	141,581		$	397,120		$	76,611		$	2,489		$	617,801
Weighted average yield	2.42		%	2.67		%	2.93		%	2.88		%	2.65		%
Full tax-equivalent yield	2.63		%	2.87		%	3.93		%	3.79		%	2.96		%
Held to Maturity:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	19,536		$	5,027		$	—		$	—		$	24,563
Weighted average yield	1.93		%	2.06		%	—		%	—		%	1.96		%
Full tax-equivalent yield	1.93		%	2.06		%	—		%	—		%	1.96		%

The weighted average yields are calculated on the basis of the amortized cost and effective yields weighted for the scheduled maturity of each security. Tax-equivalent yields have been calculated using a 21% tax rate. With the exception of obligations of the U.S. Treasury and other U.S. government agencies and corporations, there were no investment securities of any single issuer, the book value of which exceeded 10% of stockholders' equity at March 31, 2020.

Investment securities carried at approximately $582 million and $688 million at March 31, 2020 and December 31, 2019, respectively, were pledged to secure public deposits and repurchase agreements and for other purposes as permitted or required by law.

The following table presents the aging of gross unrealized losses and fair value by investment category as of March 31, 2020 and December 31, 2019 (in thousands):



	Less than 12 months					12 months or more					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
March 31, 2020
Available-for-sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	5,802	$	(94	)	$	—	$	—		$	5,802	$	(94	)
Obligations of states and political subdivisions	119,614		(3,904		)	—		—			119,614		(3,904		)
Mortgage-backed securities: GSE residential	51,736		(315		)	3,679		(85		)	55,415		(400		)
Other securities	709		(41		)	—		—			709		(41		)
Total	$	177,861	$	(4,354	)	$	3,679	$	(85	)	$	181,540	$	(4,439	)
December 31, 2019
Available-for-sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	23,375	$	(60	)	$	—	$	—		$	23,375	$	(60	)
Obligations of states and political subdivisions	3,469		(16		)	347		(1		)	3,816		(17		)
Mortgage-backed securities: GSE residential	67,080		(322		)	20,888		(190		)	87,968		(512		)
Total	$	93,924	$	(398	)	$	21,235	$	(191	)	$	115,159	$	(589	)
Held-to-maturity:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	14,996	$	(25	)	$	24,565	$	(44	)	$	39,561	$	(69	)

U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies. At March 31, 2020 and December 31, 2019, there were no available-for sale U.S. Treasury securities and obligations of U.S. government corporations and agencies in a continuous unrealized loss position for twelve months or more. At December 31, 2019, there were four held-to-maturity U.S. Treasury securities and obligations of U.S. government corporations and agencies with a fair value of $24,565,000 and unrealized losses of $44,000 in a continuous unrealized loss position for twelve months or more.

Obligations of states and political subdivisions. At March 31, 2020, there were no obligations of states and political subdivisions in a continuous loss position for twelve months or more. At December 31, 2019, there was one obligation of states and political subdivisions with a fair value of $347,000 and unrealized losses of $1,000 in a continuous unrealized loss position for twelve months or more.

Mortgage-backed Securities: GSE Residential. At March 31, 2020, there were five mortgage-backed securities with a fair value of $3,679,000 and unrealized losses of $85,000 in a continuous unrealized loss position for twelve months or more. At December 31, 2019, there were fourteen mortgage-backed securities with a fair value of $20,888,000 and unrealized losses of $190,000 in a continuous unrealized loss position for twelve months or more.

The Company does not believe any other individual unrealized loss as of March 31, 2020 represents other than temporary impairment ("OTTI"). However, given the uncertainty of the financial markets, the Company may be required to recognize OTTI losses in future periods with respect to its available for sale investment securities portfolio. The amount and timing of any additional OTTI will depend on the decline in the underlying cash flows of the securities. 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 the period the other-than-temporary impairment is identified.