
	September 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available for Sale	(in thousands)


State and municipal securities	$	880,495	$	46,216	$	(157)	$	926,554
Corporate debt securities	327,143		16,724		(1,309)		342,558
Collateralized mortgage obligations	516,312		16,207		(46)		532,473
Residential mortgage-backed securities	318,343		3,409		(57)		321,695
Commercial mortgage-backed securities	548,076		24,136		(2)		572,210
Auction rate securities	101,510		—		(3,520)		97,990


Total	$	2,691,879	$	106,692	$	(5,091)	$	2,793,480

Held to Maturity

Residential mortgage-backed securities	$	304,241	$	20,699	$	—	$	324,940


	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available for Sale	(in thousands)


State and municipal securities	$	638,125	$	15,826	$	(1,024)	$	652,927
Corporate debt securities	370,401		8,490		(1,534)		377,357
Collateralized mortgage obligations	682,307		11,726		(315)		693,718
Residential mortgage-backed securities	177,183		1,078		(949)		177,312
Commercial mortgage-backed securities	489,603		6,471		(1,777)		494,297
Auction rate securities	107,410		—		(5,484)		101,926
Total	$	2,465,029	$	43,591	$	(11,083)	$	2,497,537



Held to Maturity

Residential mortgage-backed securities	$	369,841	$	13,864	$	—	$	383,705

On July 1, 2019, the Corporation transferred state and municipal securities from the held to maturity classification to the available for sale classification as permitted through the early adoption of ASU 2019-04. The amortized cost of the securities transferred was $158.9 million and the estimated fair value was $168.5 million.

Securities carried at $568.4 million at September 30, 2020 and $462.6 million at December 31, 2019 were pledged as collateral to secure public and trust deposits and customer repurchase agreements.

The amortized cost and estimated fair values of debt securities as of September 30, 2020, by contractual maturity, are shown in the following table. Actual maturities may differ from contractual maturities as certain investment securities are subject to call or prepayment with or without call or prepayment penalties.


		September 30, 2020
		Available for Sale				Held to Maturity
		Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(in thousands)
Due in one year or less		$	11,252	$	11,388	$	—	$	—
Due from one year to five years		32,118		33,397		—		—
Due from five years to ten years		315,094		330,233		—		—
Due after ten years		950,684		992,084		—		—
		1,309,148		1,367,102		—		—
Residential mortgage-backed securities(1)		318,343		321,695		304,241		324,940
Commercial mortgage-backed securities(1)		548,076		572,210		—		—
Collateralized mortgage obligations(1)		516,312		532,473		—		—
Total		$	2,691,879	$	2,793,480	$	304,241	$	324,940

(1) Mortgage-backed securities and collateralized mortgage obligations do not have stated maturities and are dependent upon the interest rate environment and prepayments on the underlying loans.


	Gross Realized Gains		Gross Realized Losses		Net Gains
Three months ended	(in thousands)
September 30, 2020	$	94	$	(92)	$	2
September 30, 2019	7,938		(3,446)		4,492

Nine months ended
September 30, 2020	$	6,545	$	(3,492)	$	3,053
September 30, 2019	11,207		(6,474)		4,733

During the second quarter of 2020, the Corporation completed a limited balance sheet restructuring that included the sale of investment securities, with an amortized cost $79.0 million and an estimated fair value of $82.0 million, resulting in net investment securities gains of $3.0 million. Offsetting these gains were $2.9 million of prepayment penalties recorded in non-interest expense for the redemption of FHLB advances.

During the third quarter of 2019, the Corporation completed a balance sheet restructuring that included the sale of investment securities, with an amortized cost of $409.2 million and an estimated fair value of $413.7 million, resulting in net investment securities gains of $4.5 million. Offsetting these gains were $4.3 million of prepayment penalties recorded in non-interest expense for the redemption of FHLB advances.

The following tables present the gross unrealized losses and estimated fair values of investment securities, aggregated by category and length of time that individual securities have been in a continuous unrealized loss position for the periods presented:


	September 30, 2020
	Less than 12 months					12 months or longer					Total
	Number of Securities	Estimated Fair Value		Unrealized Losses		Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses

Available for Sale		(in thousands)

State and municipal securities	6	$	25,372	$	(157)	—	$	—	$	—	$	25,372	$	(157)
Corporate debt securities	16	67,030		(965)		1	6,847		(344)		73,877		(1,309)
Collateralized mortgage obligations	1	25,489		(46)		—	—		—		25,489		(46)
Residential mortgage-backed securities	4	75,876		(57)		—	—		—		75,876		(57)
Commercial mortgage-backed securities	1	9,322		(2)		—	—		—		9,322		(2)
Auction rate securities	—	—		—		162	97,990		(3,520)		97,990		(3,520)
Total available for sale(1)	28	$	203,089	$	(1,227)	163	$	104,837	$	(3,864)	$	307,926	$	(5,091)


	December 31, 2019
	Less than 12 months					12 months or longer					Total
	Number of Securities	Estimated Fair Value		Unrealized Losses		Number of Securities	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
Available for Sale	(in thousands)

State and municipal securities	44	$	136,344	$	(1,024)	—	$	—	$	—	$	136,344	$	(1,024)
Corporate debt securities	5	30,719		(346)		8	18,759		(1,188)		49,478		(1,534)
Collateralized mortgage obligations	5	33,865		(190)		1	5,330		(125)		39,195		(315)
Residential mortgage-backed securities	5	12,247		(40)		26	127,373		(909)		139,620		(949)
Commercial mortgage-backed securities	7	121,340		(1,777)		—	—		—		121,340		(1,777)
Auction rate securities	—	—		—		177	101,926		(5,484)		101,926		(5,484)
Total available for sale(1)	66	$	334,515	$	(3,377)	212	$	253,388	$	(7,706)	$	587,903	$	(11,083)

The Corporation’s collateralized mortgage obligations and mortgage-backed securities have contractual terms that generally do not permit the issuer to settle the securities at a price less than the amortized cost of the investment. The change in fair value of these securities is attributable to changes in interest rates and not credit quality. The Corporation does not have the intent to sell and does not believe it will more likely than not be required to sell any of these securities prior to a recovery of their fair value to amortized cost. Therefore, the Corporation does not have an ACL for these investments as of September 30, 2020.