

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Available for sale at March 31, 2019
U.S. Government-sponsored agency securities	$	33,494	$	210	$	1	$	33,703
State and municipal	633,617		18,773		532		651,858
U.S. Government-sponsored mortgage-backed securities	562,587		2,592		3,139		562,040
Corporate obligations	31		—		—		31
Total available for sale	1,229,729		21,575		3,672		1,247,632
Held to maturity at March 31, 2019
U.S. Government-sponsored agency securities	22,619		—		350		22,269
State and municipal	254,520		6,682		117		261,085
U.S. Government-sponsored mortgage-backed securities	336,888		2,630		1,237		338,281
Foreign investment	1,000		—		—		1,000
Total held to maturity	615,027		9,312		1,704		622,635
Total Investment Securities	$	1,844,756	$	30,887	$	5,376	$	1,870,267



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Available for sale at December 31, 2018
U.S. Government-sponsored agency securities	$	13,493	$	92	$	3	$	13,582
State and municipal	605,994		5,995		5,854		606,135
U.S. Government-sponsored mortgage-backed securities	530,209		634		8,396		522,447
Corporate obligations	31		—		—		31
Total available for sale	1,149,727		6,721		14,253		1,142,195
Held to maturity at December 31, 2018
U.S. Government-sponsored agency securities	22,618		—		545		22,073
State and municipal	197,909		2,858		872		199,895
U.S. Government-sponsored mortgage-backed securities	268,860		713		3,323		266,250
Foreign investment	1,000		—		1		999
Total held to maturity	490,387		3,571		4,741		489,217
Total Investment Securities	$	1,640,114	$	10,292	$	18,994	$	1,631,412

The change in unrealized gains/losses from December 31, 2018 to March 31, 2019 is primarily due to the changes in interest rates. The longer term points on the yield curve have declined since year-end which increases the fair value of securities held in the portfolio.

The amortized cost and fair value of available for sale and held to maturity securities at March 31, 2019 and December 31, 2018, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties.



	Available for Sale				Held to Maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Maturity Distribution at March 31, 2019:
Due in one year or less	$	4,746	$	4,764	$	3,502	$	3,501
Due after one through five years	3,750		3,835		49,060		48,717
Due after five through ten years	79,533		81,458		65,990		68,332
Due after ten years	579,113		595,535		159,587		163,804
	667,142		685,592		278,139		284,354
U.S. Government-sponsored mortgage-backed securities	562,587		562,040		336,888		338,281
Total Investment Securities	$	1,229,729	$	1,247,632	$	615,027	$	622,635



	Available for Sale				Held to Maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Maturity Distribution at December 31, 2018
Due in one year or less	$	13,092	$	13,144	$	4,732	$	4,730
Due after one through five years	5,311		5,378		49,054		48,473
Due after five through ten years	73,280		74,411		62,873		64,163
Due after ten years	527,835		526,815		104,868		105,601
	619,518		619,748		221,527		222,967
U.S. Government-sponsored mortgage-backed securities	530,209		522,447		268,860		266,250
Total Investment Securities	$	1,149,727	$	1,142,195	$	490,387	$	489,217

The following tables show the Corporation’s gross unrealized losses and fair value, aggregated by investment category and length of time the individual securities have been in a continuous unrealized loss position at March 31, 2019, and December 31, 2018:



	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Temporarily Impaired Available for Sale Securities at March 31, 2019
U.S. Government-sponsored agency securities	$	—	$	—	$	373	$	1	$	373	$	1
State and municipal	—		—		31,483		532		31,483		532
U.S. Government-sponsored mortgage-backed securities	3,761		2		310,455		3,137		314,216		3,139
Total Temporarily Impaired Available for Sale Securities	3,761		2		342,311		3,670		346,072		3,672
Temporarily Impaired Held to Maturity Securities at March 31, 2019
U.S. Government-sponsored agency securities	—		—		22,269		350		22,269		350
State and municipal	310		—		13,200		117		13,510		117
U.S. Government-sponsored mortgage-backed securities	479		—		105,396		1,237		105,875		1,237
Foreign investment	—		—		1,000		—		1,000		—
Total Temporarily Impaired Held to Maturity Securities	789		—		141,865		1,704		142,654		1,704
Total Temporarily Impaired Investment Securities	$	4,550	$	2	$	484,176	$	5,374	$	488,726	$	5,376



	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Temporarily Impaired Available for Sale Securities at December 31, 2018
U.S. Government-sponsored agency securities	$	1,490	$	3	$	—	$	—	$	1,490	$	3
State and municipal	234,431		3,958		38,028		1,896		272,459		5,854
U.S. Government-sponsored mortgage-backed securities	196,601		2,400		217,121		5,996		413,722		8,396
Total Temporarily Impaired Available for Sale Securities	432,522		6,361		255,149		7,892		687,671		14,253
Temporarily Impaired Held to Maturity Securities at December 31, 2018
U.S. Government-sponsored agency securities	—		—		22,073		545		22,073		545
State and municipal	14,952		369		16,786		503		31,738		872
U.S. Government-sponsored mortgage-backed securities	102,828		876		87,268		2,447		190,096		3,323
Foreign investment	—		—		999		1		999		1
Total Temporarily Impaired Held to Maturity Securities	117,780		1,245		127,126		3,496		244,906		4,741
Total Temporarily Impaired Investment Securities	$	550,302	$	7,606	$	382,275	$	11,388	$	932,577	$	18,994



	March 31, 2019			December 31, 2018
Investments reported at less than historical cost:
Historical cost	$	494,102		$	951,571
Fair value	488,726			932,577
Gross unrealized losses	$	5,376		$	18,994
Percent of the Corporation's investment portfolio	26.2		%	57.1		%

The Corporation's management believes the decline in fair value for these securities was temporary. 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 net income during the period the other-than-temporary-impairment ("OTTI") is identified. The Corporation’s management has evaluated all securities with unrealized losses for OTTI and concluded no OTTI existed at March 31, 2019.

In determining the fair value of the investment securities portfolio, the Corporation utilizes a third party for portfolio accounting services, including market value input, for those securities classified as Level 1 and Level 2 in the fair value hierarchy. The Corporation has obtained an understanding of what inputs are being used by the vendor in pricing the portfolio and how the vendor classified these securities based upon these inputs. From these discussions, the Corporation’s management is comfortable that the classifications are proper. The Corporation has gained trust in the data for two reasons: (a) independent spot testing of the data is conducted by the Corporation through obtaining market quotes from various brokers on a periodic basis; and (b) actual gains or loss resulting from the sale of certain securities has proven the data to be accurate over time. Fair value of securities classified as Level 3 in the valuation hierarchy was determined using a discounted cash flow model that incorporated market estimates of interest rates and volatility in markets that have not been active.

The unrealized losses on the Corporation's investments in securities of state and political subdivisions and U.S. Government-Sponsored Agency securities were caused by interest rate increases. The contractual terms of those investments do not permit the issuer to settle the securities at a price less than the amortized cost basis of the investments. Because the Corporation does not intend to sell the investments and it is not more likely than not that the Corporation will be required to sell the investments before recovery of their amortized cost basis, which may be maturity, the Corporation does not consider those investments to be other-than-temporarily impaired at March 31, 2019. The state and municipal securities portfolio contains unrealized losses of $532,000 on thirty-three securities and $117,000 on twenty-two securities in the available for sale and held to maturity portfolios, respectively. The U.S. Government-Sponsored Agency securities portfolio contains unrealized losses of $1,000 on one security and $350,000 on five securities in the available for sale and held to maturity portfolios, respectively.