Investment Securities (Tables)

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

The following is a summary of the amortized cost and fair value of investment securities carried at fair value and investment securities held-to-maturity at December 31, 2018 and 2017:



	Investment Securities Carried at Fair Value
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
December 31, 2018
Debt securities
Government and government-sponsored enterprises	$	354,342	$	713	$	3,355	$	351,700
State and political subdivisions	523,178		1,141		8,033		516,286
Residential mortgage-backed securities	216,990		261		3,823		213,428
Collateralized mortgage obligations	1,623,415		2,903		25,020		1,601,298
Corporate bonds	304,243		259		11,439		293,063
Trust preferred securities	47,477		324		1,744		46,057
Total	$	3,069,645	$	5,601	$	53,414	$	3,021,832
December 31, 2017
Debt securities
Government and government-sponsored enterprises	$	203,099	$	765	$	948	$	202,916
State and political subdivisions	350,088		310		4,428		345,970
Residential mortgage-backed securities	151,752		5		1,626		150,131
Collateralized mortgage obligations	1,042,240		89		8,484		1,033,845
Corporate bonds	193,230		1,156		1,592		192,794
Trust preferred securities	34,848		1,280		62		36,066
Total debt securities available-for-sale	1,975,257		3,605		17,140		1,961,722
Equity securities
Preferred stock	1,389		435		—		1,824
Total equity securities	1,389		435		—		1,824
Total	$	1,976,646	$	4,040	$	17,140	$	1,963,546

Held-to-maturity Securities



	Investment Securities Held-to-Maturity
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
December 31, 2018
State and political subdivisions	$	623,599	$	2,548	$	7,915	$	618,232
Trust preferred securities	500		—		60		440
Total	$	624,099	$	2,548	$	7,975	$	618,672
December 31, 2017
State and political subdivisions	$	676,593	$	3,856	$	17,933	$	662,516
Trust preferred securities	500		—		110		390
Total	$	677,093	$	3,856	$	18,043	$	662,906

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

Proceeds from sales of investment securities carried at fair value and the associated gains and losses recorded in earnings are listed below:



	For the years ended December 31,
(Dollars in thousands)	2018			2017			2016
Proceeds	$	4,215		$	409,220		$	41,446
Gross gains	263			178			325
Gross losses	(39		)	(7,566		)	(196		)

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 December 31, 2018, by maturity, for both carried at fair value and held-to-maturity. 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, 2018
(Dollars in thousands)	Amortized Cost		Fair Value
Investment Securities Carried at Fair Value:
Due in one year or less	$	51,523	$	51,244
Due after one year through five years	109,918		108,051
Due after five years through ten years	515,050		498,612
Due after ten years	2,393,154		2,363,925
Total	$	3,069,645	$	3,021,832
Investment Securities Held-to-Maturity:
Due in one year or less	$	55,840	$	55,728
Due after one year through five years	230,154		228,528
Due after five years through ten years	164,325		162,764
Due after ten years	173,780		171,652
Total	$	624,099	$	618,672

Summary of continuous unrealized loss position of securities

The following schedule summarizes information for debt securities both carried at fair value and held-to-maturity with gross unrealized losses at December 31, 2018 and 2017, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position. As of December 31, 2018, the Corporation's securities portfolio consisted of 2,096 securities, 1,408 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, 2018
Government and government-sponsored enterprises	$	167,164	$	1,672	$	62,200	$	1,683	$	229,364	$	3,355
State and political subdivisions	190,551		1,932		657,327		14,016		847,878		15,948
Residential mortgage-backed securities	20,679		85		123,757		3,738		144,436		3,823
Collateralized mortgage obligations	496,356		5,268		656,208		19,752		1,152,564		25,020
Corporate bonds	169,431		5,888		103,688		5,551		273,119		11,439
Trust preferred securities	34,623		1,640		2,725		164		37,348		1,804
Total	$	1,078,804	$	16,485	$	1,605,905	$	44,904	$	2,684,709	$	61,389
December 31, 2017
Government and government-sponsored enterprises	$	63,818	$	510	$	24,621	$	438	$	88,439	$	948
State and political subdivisions	437,407		12,268		349,242		10,093		786,649		22,361
Residential mortgage-backed securities	93,508		383		56,576		1,243		150,084		1,626
Collateralized mortgage obligations	713,525		7,235		73,707		1,249		787,232		8,484
Corporate bonds	71,447		1,138		47,878		454		119,325		1,592
Trust preferred securities	—		—		11,164		172		11,164		172
Total	$	1,379,705	$	21,534	$	563,188	$	13,649	$	1,942,893	$	35,183