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 June 30, 2017 and December 31, 2016:



	Investment Securities Available-for-Sale
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
June 30, 2017
U.S. Treasury securities	$	5,795	$	—	$	2	$	5,793
Government sponsored agencies	248,021		619		1,166		247,474
State and political subdivisions	297,560		114		5,639		292,035
Residential mortgage-backed securities	296,898		26		4,012		292,912
Collateralized mortgage obligations	737,963		173		4,949		733,187
Corporate bonds	158,828		276		936		158,168
Preferred stock and trust preferred securities	36,070		1,871		32		37,909
Total	$	1,781,135	$	3,079	$	16,736	$	1,767,478
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



	Investment Securities Held-to-Maturity
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
June 30, 2017
State and political subdivisions	$	645,105	$	5,281	$	10,703	$	639,683
Trust preferred securities	500		—		140		360
Total	$	645,605	$	5,281	$	10,843	$	640,043
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

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:



	Three Months Ended June 30,				Six Months Ended June 30,
(Dollars in thousands)	2017		2016		2017		2016
Proceeds	$	10,050	$	4,356	$	10,050	$	5,000
Gross gains	77		18		167		37

The following is a summary of the amortized cost and fair value of investment securities at June 30, 2017, 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.



	June 30, 2017
(Dollars in thousands)	Amortized Cost		Fair Value
Investment Securities Available-for-Sale:
Due in one year or less	$	345,833	$	344,064
Due after one year through five years	731,523		726,231
Due after five years through ten years	488,832		485,107
Due after ten years	213,558		210,229
Preferred stock	1,389		1,847
Total	$	1,781,135	$	1,767,478
Investment Securities Held-to-Maturity:
Due in one year or less	$	85,434	$	85,398
Due after one year through five years	253,002		251,488
Due after five years through ten years	143,396		141,140
Due after ten years	163,773		162,017
Total	$	645,605	$	640,043

Securities with a carrying value of $1.05 billion and $794.0 million were pledged at June 30, 2017 and December 31, 2016, respectively, to secure borrowings and deposits.

At June 30, 2017 and December 31, 2016, there were no holdings of securities of any one issuer, other than the 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 June 30, 2017 and December 31, 2016, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position. As of June 30, 2017, the Corporation’s securities portfolio consisted of 2,336 securities, 1,351 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
June 30, 2017
U.S. Treasury securities	$	5,793	$	2	$	—	$	—	$	5,793	$	2
Government sponsored agencies	104,655		1,042		10,816		124		115,471		1,166
State and political subdivisions	614,276		15,504		46,588		838		660,864		16,342
Residential mortgage-backed securities	284,277		4,012		—		—		284,277		4,012
Collateralized mortgage obligations	627,054		4,765		11,061		184		638,115		4,949
Corporate bonds	111,931		935		1,499		1		113,430		936
Trust preferred securities	3,843		32		360		140		4,203		172
Total	$	1,751,829	$	26,292	$	70,324	$	1,287	$	1,822,153	$	27,579
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

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, as of June 30, 2017, represented 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 June 30, 2017 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 June 30, 2017, 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 June 30, 2017, 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.