SECURITIES

The amortized cost and estimated fair value of securities available for sale along with gross unrealized gains and losses are summarized as follows:



(dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
December 31, 2017
State, county and municipal securities	135,968		1,989		(163		)	137,794
Corporate debt securities	46,659		721		(237		)	47,143
Mortgage-backed securities	630,666		1,762		(6,492		)	625,936
Total debt securities	$	813,293	$	4,472	$	(6,892	)	$	810,873

December 31, 2016
U.S. government sponsored agencies	$	999	$	21	$	—		$	1,020
State, county and municipal securities	149,899		2,605		(469		)	152,035
Corporate debt securities	32,375		167		(370		)	32,172
Mortgage-backed securities	641,362		2,700		(6,554		)	637,508
Total debt securities	$	824,635	$	5,493	$	(7,393	)	$	822,735

The following table shows the gross unrealized losses and estimated fair value of securities aggregated by category and length of time that securities have been in a continuous unrealized loss position at December 31, 2017 and 2016.



	Less Than 12 Months					12 Months or More					Total
(dollars in thousands)	Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
December 31, 2017
State, county and municipal securities	33,976		(115		)	4,725		(48		)	38,701		(163		)
Corporate debt securities	3,465		(35		)	18,853		(202		)	22,318		(237		)
Mortgage-backed securities	262,353		(2,401		)	190,368		(4,091		)	452,721		(6,492		)
Total debt securities	$	299,794	$	(2,551	)	$	213,946	$	(4,341	)	$	513,740	$	(6,892	)

December 31, 2016
State, county and municipal securities	47,647		(469		)	—		—			47,647		(469		)
Corporate debt securities	18,377		(363		)	493		(7		)	18,870		(370		)
Mortgage-backed securities	414,300		(6,177		)	11,791		(377		)	$	426,091	(6,554		)
Total debt securities	$	480,324	$	(7,009	)	$	12,284	$	(384	)	$	492,608	$	(7,393	)

As of December 31, 2017, the Company’s security portfolio consisted of 418 securities, 215 of which were in an unrealized loss position. The majority of the unrealized losses are related to the Company’s mortgage-backed securities as discussed below.

At December 31, 2017, the Company held 181 mortgage-backed securities that were in an unrealized loss position, all of which were issued by U.S. government-sponsored entities and agencies. Because the decline in fair value is attributable to changes in interest rates and illiquidity, and not credit quality, and because the Company does not have the intent to sell these mortgage-backed securities and it is likely that it will not be required to sell the securities before their anticipated recovery, the Company does not consider these securities to be other-than-temporarily impaired at December 31, 2017.

At December 31, 2017, the Company held 24 state, county and municipal securities and 10 corporate securities that were in an unrealized loss position. Because the decline in fair value is attributable to changes in interest rates, and not credit quality, and because the Company does not have the intent to sell these securities and it is likely that it will not be required to sell the securities before their anticipated recovery, the Company does not consider these securities to be other-than-temporarily impaired at December 31, 2017.

During 2017 and 2016, the Company received timely and current interest and principal payments on all of the securities classified as corporate debt securities. During the third quarter of 2015, the Company received all interest payments due on a security that had previously deferred interest since the fourth quarter of 2010. The Company’s investments in subordinated debt include investments in regional and super-regional banks on which the Company prepares regular analysis through review of financial information or credit ratings. Investments in preferred securities are also concentrated in the preferred obligations of regional and super-regional banks through non-pooled investment structures. The Company did not have investments in “pooled” trust preferred securities at December 31, 2017 or 2016.

Management and the Company’s Asset and Liability Committee (the “ALCO Committee”) evaluate securities for other-than-temporary impairment at least on a quarterly basis, and more frequently when economic or market concerns warrant such evaluation. While the majority of the unrealized losses on debt securities relate to changes in interest rates, corporate debt securities have also been affected by reduced levels of liquidity and higher risk premiums. Occasionally, management engages independent third parties to evaluate the Company’s position in certain corporate debt securities to aid management and the ALCO Committee in its determination regarding the status of impairment. The Company believes that each investment poses minimal credit risk and further, that the Company does not intend to sell these investment securities at an unrealized loss position at December 31, 2017, and it is more likely than not that the Company will not be required to sell these securities prior to recovery or maturity. Therefore, at December 31, 2017, these investments are not considered impaired on an other-than-temporary basis.

At December 31, 2017 and 2016, all of the Company’s mortgage-backed securities were obligations of government-sponsored entities and agencies.

The amortized cost and estimated fair value of debt securities available for sale as of December 31, 2017, by contractual maturity are shown below. Maturities may differ from contractual maturities in mortgage-backed securities because the mortgages underlying the securities may be called or repaid without penalty. Securities not due at a single maturity date are shown separately. Therefore, these securities are not included in the maturity categories in the following maturity summary.



(dollars in thousands)	Amortized Cost		Estimated Fair Value
Due in one year or less	$	11,510	$	11,562
Due from one year to five years	58,549		58,881
Due from five to ten years	73,566		74,861
Due after ten years	39,002		39,633
Mortgage-backed securities	630,666		625,936
	$	813,293	$	810,873

Securities with a carrying value of approximately $403.3 million and $618.2 million at December 31, 2017 and 2016, respectively, serve as collateral to secure public deposits, securities sold under agreements to repurchase and for other purposes required or permitted by law.

Gains and losses on sales of securities available for sale consist of the following:



	For the Years Ended December 31,
(dollars in thousands)	2017			2016			2015
Gross gains on sales of securities	$	38		$	312		$	396
Gross losses on sales of securities	(1		)	(218		)	(259		)
Net realized gains on sales of securities available for sale	$	37		$	94		$	137