Investment Securities

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 March 31, 2019 and December 31, 2018:



	Investment Securities Carried at Fair Value
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
March 31, 2019
Debt securities
Government and government-sponsored enterprises	$	389,657	$	357	$	2,624	$	387,390
State and political subdivisions	545,823		10,100		1,180		554,743
Residential mortgage-backed securities	203,692		836		2,288		202,240
Collateralized mortgage obligations	1,812,649		5,943		15,668		1,802,924
Corporate bonds	312,112		205		6,170		306,147
Trust preferred securities	47,577		555		522		47,610
Total	$	3,311,510	$	17,996	$	28,452	$	3,301,054
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



	Investment Securities Held-to-Maturity
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
March 31, 2019
State and political subdivisions	$	622,019	$	7,392	$	2,246	$	627,165
Trust preferred securities	500		—		50		450
Total	$	622,519	$	7,392	$	2,296	$	627,615
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

Investment securities are classified at the time they are acquired as either available-for-sale, held-to-maturity or carried at fair value based upon various factors, including asset/liability management strategies, liquidity and profitability objectives and regulatory requirements. Debt securities classified as available-for-sale are recorded at fair value. Investment securities carried at fair value may be sold prior to maturity based upon asset/liability management decisions. Unrealized gains or losses on available-for-sale debt securities are recorded as part of accumulated other comprehensive income in stockholders' equity. Held-to-maturity securities are carried at amortized cost, adjusted for amortization of premiums or accretion of discounts.

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



	Three Months Ended March 31,
(Dollars in thousands)	2019			2018
Proceeds	$	71,502		$	—
Gross gains	552			—
Gross losses	(465		)	—

The following is a summary of the amortized cost and fair value of investment securities at March 31, 2019, 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.



	March 31, 2019
(Dollars in thousands)	Amortized Cost		Fair Value
Investment Securities Carried at Fair Value:
Due in one year or less	$	47,145	$	47,088
Due after one year through five years	85,636		84,973
Due after five years through ten years	537,851		530,965
Due after ten years	2,640,878		2,638,028
Total	$	3,311,510	$	3,301,054
Investment Securities Held-to-Maturity:
Due in one year or less	$	55,696	$	55,676
Due after one year through five years	229,594		230,314
Due after five years through ten years	162,812		165,238
Due after ten years	174,417		176,387
Total	$	622,519	$	627,615

Securities with a carrying value of $971.1 million and $1.05 billion were pledged at March 31, 2019 and December 31, 2018, respectively, to secure borrowings and deposits.

At March 31, 2019 and December 31, 2018, 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 debt securities both carried at fair value and held-to-maturity with gross unrealized losses at March 31, 2019 and December 31, 2018, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position. As of March 31, 2019, the Corporation's securities portfolio consisted of 2,087 securities, 879 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
March 31, 2019
Government and government-sponsored enterprises	$	120,690	$	937	$	112,261	$	1,687	$	232,951	$	2,624
State and political subdivisions	15,474		32		424,934		3,394		440,408		3,426
Residential mortgage-backed securities	1,217		5		120,950		2,283		122,167		2,288
Collateralized mortgage obligations	170,414		1,093		873,914		14,575		1,044,328		15,668
Corporate bonds	117,903		1,003		162,324		5,167		280,227		6,170
Trust preferred securities	25,034		433		2,752		139		27,786		572
Total	$	450,732	$	3,503	$	1,697,135	$	27,245	$	2,147,867	$	30,748
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

An assessment is performed quarterly by the Corporation to determine whether unrealized losses in its debt 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 debt security, as of March 31, 2019, 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 debt securities at March 31, 2019 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 March 31, 2019, the Corporation did not have the intent to sell any of its impaired debt securities and believed that it was more-likely-than-not that the Corporation will not have to sell any such debt securities before a full recovery of amortized cost. Accordingly, at March 31, 2019, the Corporation believed the impairments in its debt securities portfolio were temporary in nature. However, there is no assurance that OTTI may not occur in the future.