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


State and municipal securities	$	852,617	$	41,292	$	(227)	$	893,682
Corporate debt securities	312,507		15,168		(2,322)		325,353
Collateralized mortgage obligations	559,281		19,113		—		578,394
Residential mortgage-backed securities	156,152		4,716		—		160,868
Commercial mortgage-backed securities	560,294		24,849		—		585,143
Auction rate securities	107,410		—		(6,551)		100,859


Total	$	2,548,261	$	105,138	$	(9,100)	$	2,644,299

Held to Maturity

Residential mortgage-backed securities	$	330,514	$	23,595	$	—	$	354,109


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


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

Securities carried at $468.8 million at June 30, 2020 and $462.6 million at December 31, 2019 were pledged as collateral to secure public and trust deposits and customer repurchase agreements.

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.

The amortized cost and estimated fair values of debt securities as of June 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.


		Available for Sale						Held to Maturity
		Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(in thousands)
Due in one year or less		$	12,731	$	12,731	$	—	$	—
Due from one year to five years		31,144		32,687		—		—
Due from five years to ten years		301,186		313,583		—		—
Due after ten years		927,473		960,893		—		—
		1,272,534		1,319,894		—		—
Residential mortgage-backed securities⁽¹⁾		156,152		160,868		330,514		354,109
Commercial mortgage-backed securities⁽¹⁾		560,294		585,143		—		—
Collateralized mortgage obligations⁽¹⁾		559,281		578,394		—		—
Total		$	2,548,261	$	2,644,299	$	330,514	$	354,109

(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
	(in thousands)
Three months ended
June 30, 2020	$	6,334	$	(3,329)	$	3,005
June 30, 2019	3,012		(2,836)		176

Six months ended
June 30, 2020	$	6,451	$	(3,400)	$	3,051
June 30, 2019	3,269		(3,028)		241

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 as of June 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	9	$	30,378	$	(227)	—	$	—	$	—	$	30,378	$	(227)
Corporate debt securities	15	85,486		(2,322)		—	—		—		85,486		(2,322)



Auction rate securities	—	—		—		177	100,859		(6,551)		100,859		(6,551)
Total available for sale⁽¹⁾	24	$	115,864	$	(2,549)	177	$	100,859	$	(6,551)	$	216,723	$	(9,100)


	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, and 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 June 30, 2020.