Investment Securities

The following is a summary of the amortized cost and fair value of investment securities available-for-sale and investment securities held-to-maturity at December 31, 2016 and 2015:



	Investment Securities Available-for-Sale
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
December 31, 2016
U.S. Treasury securities	$	5,788	$	5	$	—	$	5,793
Government sponsored agencies	216,890		189		2,068		215,011
State and political subdivisions	311,704		163		11,779		300,088
Residential mortgage-backed securities	276,162		112		3,992		272,282
Collateralized mortgage obligations	323,965		63		4,003		320,025
Corporate bonds	90,859		16		1,401		89,474
Preferred stock and trust preferred securities	31,353		1,018		80		32,291
Total	$	1,256,721	$	1,566	$	23,323	$	1,234,964
December 31, 2015
U.S. Treasury securities	$	5,773	$	—	$	8	$	5,765
Government sponsored agencies	195,711		78		800		194,989
State and political subdivisions	14,731		395		6		15,120
Residential mortgage-backed securities	189,452		538		2,222		187,768
Collateralized mortgage obligations	133,256		111		1,137		132,230
Corporate bonds	14,825		2		200		14,627
Preferred stock and trust preferred securities	2,888		344		—		3,232
Total	$	556,636	$	1,468	$	4,373	$	553,731



	Investment Securities Held-to-Maturity
(Dollars in thousands)	Amortized Cost		Unrecognized Gains		Unrecognized Losses		Fair Value
December 31, 2016
State and political subdivisions	$	622,927	$	2,648	$	17,354	$	608,221
Trust preferred securities	500		—		190		310
Total	$	623,427	$	2,648	$	17,544	$	608,531
December 31, 2015
State and political subdivisions	$	509,471	$	7,446	$	4,512	$	512,405
Trust preferred securities	500		—		200		300
Total	$	509,971	$	7,446	$	4,712	$	512,705

The majority of the Corporation's residential mortgage-backed securities and collateralized mortgage obligations are backed by a U.S. government agency (Government National Mortgage Association) or a government sponsored enterprise (Federal Home Loan Mortgage Corporation or Federal National Mortgage Association).

Proceeds from sales of securities and the associated gains and losses recorded in earnings are listed below:



	For the years ended December 31,
(Dollars in thousands)	2016			2015			2014
Proceeds	$	41,446		$	40,301		$	—
Gross gains	325			631			—
Gross losses	(196		)	(1		)	—

The following is a summary of the amortized cost and fair value of investment securities at December 31, 2016, by maturity, for both available-for-sale and held-to-maturity investment securities. The maturities of residential mortgage-backed securities and collateralized mortgage obligations are based on scheduled principal payments. The maturities of all other debt securities are based on final contractual maturity.



	December 31, 2016
(Dollars in thousands)	Amortized Cost		Fair Value
Investment Securities Available-for-Sale:
Due in one year or less	$	237,047	$	235,845
Due after one year through five years	490,634		485,221
Due after five years through ten years	339,222		329,879
Due after ten years	188,429		182,281
Preferred stock	1,389		1,738
Total	$	1,256,721	$	1,234,964
Investment Securities Held-to-Maturity:
Due in one year or less	$	66,090	$	65,954
Due after one year through five years	262,136		257,936
Due after five years through ten years	145,225		139,320
Due after ten years	149,976		145,321
Total	$	623,427	$	608,531

Securities with a carrying value of $794.0 million and $530.8 million were pledged at December 31, 2016 and 2015, respectively, to secure borrowings and deposits.

At December 31, 2016 and 2015, there were no holdings of securities of any one issuer, other than U.S. government and its agencies, in an amount greater than 10% of shareholders' equity.

The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at December 31, 2016 and 2015, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position. As of December 31, 2016, the Corporation's securities portfolio consisted of 2,504 securities, 1,563 of which were in an unrealized loss position.



	Less Than 12 Months				12 Months or More				Total
(Dollars in thousands)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
December 31, 2016
Government sponsored agencies	$	105,702	$	1,707	$	15,023	$	361	$	120,725	$	2,068
State and political subdivisions	758,063		28,158		26,810		975		784,873		29,133
Residential mortgage-backed securities	244,239		3,992		—		—		244,239		3,992
Collateralized mortgage obligations	279,001		3,778		14,754		225		293,755		4,003
Corporate bonds	80,536		1,401		—		—		80,536		1,401
Trust preferred securities	10,699		80		310		190		11,009		270
Total	$	1,478,240	$	39,116	$	56,897	$	1,751	$	1,535,137	$	40,867
December 31, 2015
U.S. Treasury securities	$	5,765	$	8	$	—	$	—	$	5,765	$	8
Government sponsored agencies	114,640		292		21,681		508		136,321		800
State and political subdivisions	195,285		2,891		68,361		1,627		263,646		4,518
Residential mortgage-backed securities	169,226		2,146		3,435		76		172,661		2,222
Collateralized mortgage obligations	60,459		408		39,382		729		99,841		1,137
Corporate bonds	9,532		200		—		—		9,532		200
Trust preferred securities	—		—		300		200		300		200
Total	$	554,907	$	5,945	$	133,159	$	3,140	$	688,066	$	9,085

An assessment is performed quarterly by the Corporation to determine whether unrealized losses in its investment securities portfolio are temporary or other-than-temporary by carefully considering all reasonably available information. The Corporation reviews factors such as financial statements, credit ratings, news releases and other pertinent information of the underlying issuer or company to make its determination. Management did not believe any individual unrealized loss on any investment security at December 31, 2016, represented an other-than-temporary impairment (OTTI) as the unrealized losses for these securities resulted primarily from changes in benchmark U.S. Treasury interest rates and not credit issues. Management believed that the unrealized losses on investment securities at December 31, 2016 were temporary in nature and due primarily to changes in interest rates and reduced market liquidity and not as a result of credit-related issues.

At December 31, 2016, the Corporation did not have the intent to sell any of its impaired investment securities and believed that it was more-likely-than-not that the Corporation will not have to sell any such investment securities before a full recovery of amortized cost. Accordingly, at December 31, 2016, the Corporation believed the impairments in its investment securities portfolio were temporary in nature. However, there is no assurance that OTTI may not occur in the future.