Investment Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Available-for-sale 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 September 30, 2017 and December 31, 2016:

	Investment Securities Available-for-Sale
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
September 30, 2017
U.S. Treasury securities	$	5,799	$	—	$	—	$	5,799
Government sponsored agencies	278,195		969		1,316		277,848
State and political subdivisions	357,657		97		5,135		352,619
Residential mortgage-backed securities	300,501		105		3,287		297,319
Collateralized mortgage obligations	884,742		574		5,887		879,429
Corporate bonds	178,906		592		757		178,741
Preferred stock and trust preferred securities	36,154		1,836		73		37,917
Total	$	2,041,954	$	4,173	$	16,455	$	2,029,672
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

Held-to-maturity Securities

	Investment Securities Held-to-Maturity
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
September 30, 2017
State and political subdivisions	$	656,676	$	5,904	$	6,986	$	655,594
Trust preferred securities	500		—		135		365
Total	$	657,176	$	5,904	$	7,121	$	655,959
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

Proceeds from sales of securities and the associated gains and losses recorded in earnings

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

	Three Months Ended September 30,					Nine Months Ended September 30,
(Dollars in thousands)	2017		2016			2017		2016
Proceeds	$	7,035	$	2,820		$	17,085	$	7,820
Gross gains	1		17			168		54
Gross losses	—		(1		)	—		(1		)

Amortized cost and fair value of debt securities by contractual maturity

The following is a summary of the amortized cost and fair value of investment securities at September 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.

	September 30, 2017
(Dollars in thousands)	Amortized Cost		Fair Value
Investment Securities Available-for-Sale:
Due in one year or less	$	370,316	$	368,404
Due after one year through five years	794,328		789,726
Due after five years through ten years	578,043		574,481
Due after ten years	297,878		295,189
Preferred stock	1,389		1,872
Total	$	2,041,954	$	2,029,672
Investment Securities Held-to-Maturity:
Due in one year or less	$	85,395	$	85,413
Due after one year through five years	249,160		249,315
Due after five years through ten years	149,527		149,102
Due after ten years	173,094		172,129
Total	$	657,176	$	655,959

Summary of continuous unrealized loss position of securities

The following schedule summarizes information for both available-for-sale and held-to-maturity investment securities with gross unrealized losses at September 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 September 30, 2017, the Corporation’s securities portfolio consisted of 2,413 securities, 1,366 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
September 30, 2017
U.S. Treasury securities	$	2,999	$	—		$	—	$	—		$	2,999	$	—
Government sponsored agencies	111,672		(1,266		)	10,265		(50		)	121,937		(1,316		)
State and political subdivisions	506,514		(6,659		)	228,910		(5,462		)	735,424		(12,121		)
Residential mortgage-backed securities	213,620		(3,132		)	8,677		(155		)	222,297		(3,287		)
Collateralized mortgage obligations	664,682		(5,089		)	49,104		(798		)	713,786		(5,887		)
Corporate bonds	45,682		(475		)	58,123		(282		)	103,805		(757		)
Trust preferred securities	6,919		(27		)	4,195		(181		)	11,114		(208		)
Total	$	1,552,088	$	(16,648	)	$	359,274	$	(6,928	)	$	1,911,362	$	(23,576	)
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