INVESTMENTS

The following table presents the amortized cost, gross unrealized gains and losses and fair value of securities available for sale and held to maturity:



	March 31, 2018
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Available for sale securities:
Obligations of U.S. Government-sponsored enterprises	$	99,890	$	—	$	(1,698	)	$	98,192
Obligations of states and political subdivisions	32,611		386		(209		)	32,788
Agency mortgage-backed securities	524,738		360		(13,713		)	511,385
U.S. Treasury bills	9,955		—		(48		)	9,907
Total securities available for sale	$	667,194	$	746	$	(15,668	)	$	652,272
Held to maturity securities:
Obligations of states and political subdivisions	$	12,552	$	7	$	(241	)	$	12,318
Agency mortgage-backed securities	58,027		—		(1,579		)	56,448
Total securities held to maturity	$	70,579	$	7	$	(1,820	)	$	68,766



	December 31, 2017
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Available for sale securities:
Obligations of U.S. Government-sponsored enterprises	$	99,878	$	6	$	(660	)	$	99,224
Obligations of states and political subdivisions	34,181		674		(213		)	34,642
Agency mortgage-backed securities	513,082		727		(6,293		)	507,516
Total securities available for sale	$	647,141	$	1,407	$	(7,166	)	$	641,382
Held to maturity securities:
Obligations of states and political subdivisions	$	14,031	$	69	$	(46	)	$	14,054
Agency mortgage-backed securities	59,718		16		(330		)	59,404
Total securities held to maturity	$	73,749	$	85	$	(376	)	$	73,458

At March 31, 2018, and December 31, 2017, there were no holdings of securities of any one issuer in an amount greater than 10% of shareholders’ equity, other than U.S. Government agencies and sponsored enterprises. The agency mortgage-backed securities are all issued by U.S. Government-sponsored enterprises. Securities having a fair value of $401.1 million and $500.0 million at March 31, 2018, and December 31, 2017, respectively, were pledged as collateral to secure deposits of public institutions and for other purposes as required by law or contract provisions.

The amortized cost and estimated fair value of debt securities at March 31, 2018, by contractual maturity, are shown below. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. The weighted average life of the mortgage-backed securities is approximately 5 years.



	Available for sale				Held to maturity
(in thousands)	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	2,404	$	2,419	$	—	$	—
Due after one year through five years	120,488		118,875		865		858
Due after five years through ten years	14,514		14,647		10,820		10,613
Due after ten years	5,050		4,946		867		847
Agency mortgage-backed securities	524,738		511,385		58,027		56,448
	$	667,194	$	652,272	$	70,579	$	68,766

The following table represents a summary of investment securities that had an unrealized loss:



	March 31, 2018
	Less than 12 months				12 months or more				Total
(in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Obligations of U.S. Government-sponsored enterprises	$	98,192	$	1,698	$	—	$	—	$	98,192	$	1,698
Obligations of states and political subdivisions	23,766		423		361		27		24,127		450
Agency mortgage-backed securities	408,153		10,017		121,046		5,275		529,199		15,292
U.S. Treasury bills	9,907		48		—		—		9,907		48
	$	540,018	$	12,186	$	121,407	$	5,302	$	661,425	$	17,488

	December 31, 2017
	Less than 12 months				12 months or more				Total
(in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Obligations of U.S. Government-sponsored enterprises	$	89,309	$	660	$	—	$	—	$	89,309	$	660
Obligations of states and political subdivisions	13,951		259		—		—		13,951		259
Agency mortgage-backed securities	469,655		6,034		12,229		589		481,884		6,623
	$	572,915	$	6,953	$	12,229	$	589	$	585,144	$	7,542

The unrealized losses at both March 31, 2018, and December 31, 2017, were primarily attributable to changes in market interest rates since the securities were purchased. Management systematically evaluates investment securities for other-than-temporary declines in fair value on a quarterly basis. This analysis requires management to consider various factors, which include among other considerations (1) the present value of the cash flows expected to be collected compared to the amortized cost of the security, (2) duration and magnitude of the decline in value, (3) the financial condition of the issuer or issuers, (4) structure of the security, and (5) the intent to sell the security or whether it is more likely than not the Company would be required to sell the security before its anticipated recovery in market value. At March 31, 2018, management performed its quarterly analysis of all securities with an unrealized loss and concluded no individual securities were other-than-temporarily impaired.