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:



	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

	December 31, 2016
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Available for sale securities:
Obligations of U.S. Government-sponsored enterprises	$	107,312	$	348	$	—		$	107,660
Obligations of states and political subdivisions	36,486		630		(485		)	36,631
Agency mortgage-backed securities	319,345		1,101		(3,940		)	316,506
Total securities available for sale	$	463,143	$	2,079	$	(4,425	)	$	460,797

Held to maturity securities:
Obligations of states and political subdivisions	$	14,759	$	11	$	(242	)	$	14,528
Agency mortgage-backed securities	65,704		45		(638		)	65,111
Total securities held to maturity	$	80,463	$	56	$	(880	)	$	79,639

At December 31, 2017, and 2016, there were no holdings of securities of any one issuer in an amount greater than 10% of shareholders’ equity, other than the 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 $500.0 million and $407.3 million at December 31, 2017, and December 31, 2016, 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 December 31, 2017, 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 agency mortgage-backed securities is approximately 4 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	$	3,060	$	3,076	$	—	$	—
Due after one year through five years	110,910		110,480		186		195
Due after five years through ten years	14,573		14,980		12,977		12,981
Due after ten years	5,516		5,330		868		878
Agency mortgage-backed securities	513,082		507,516		59,718		59,404
	$	647,141	$	641,382	$	73,749	$	73,458

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



	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

	December 31, 2016
	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 states and political subdivisions	$	21,361	$	408	$	3,553	$	320	$	24,914	$	728
Agency mortgage-backed securities	267,734		4,084		12,883		493		280,617		4,577
	$	289,095	$	4,492	$	16,436	$	813	$	305,531	$	5,305

The unrealized losses at both December 31, 2017, and 2016, 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 that the Company would be required to sell the security before its anticipated recovery in market value. At December 31, 2017 and 2016, management performed its quarterly analysis of all securities with an unrealized loss and concluded no individual securities were other-than-temporarily impaired.

The gross gains and losses realized from sales of available for sale investment securities were as follows:



	December 31,
(in thousands)	2017		2016		2015
Gross gains realized	$	22	$	86	$	63
Gross losses realized	—		—		(40		)
Proceeds from sales	144,076		2,493		41,069

Other Investments, At Cost

At December 31, 2017, and 2016, other investments, at cost, totaled $26.7 million, and $14.8 million, respectively. As a member of the FHLB system administered by the Federal Housing Finance Agency, the Bank is required to maintain a minimum investment in capital stock with the FHLB Des Moines consisting of membership stock and activity-based stock. The FHLB capital stock of $12.9 million, and $4.4 million at December 31, 2017, and 2016, respectively, is recorded at cost, which represents redemption value, and is included in other investments in the consolidated balance sheets. The remaining amounts in other investments include various investments in SBICs and the Company's investment in unconsolidated trusts used to issue preferred securities to third parties (see Note 10 – Subordinated Debentures).