The following tables set forth the amortized cost, gross unrealized gains and losses, and estimated fair value of debt securities classified as available for sale and held to maturity at September 30, 2020 and December 31, 2019. Amortized cost of securities does not include accrued interest which is reflected in the accrued interest line item on the consolidated balance sheets totaling $23.2 million and $23.9 million at September 30, 2020 and December 31, 2019, respectively.

	September 30, 2020								December 31, 2019
			Gross		Gross				Gross		Gross
Securities Available for Sale	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and government agency securities	$	192,077	$	6,664	$	125	$	198,616	$	98,320	$	652	$	300	$	98,672
Municipal obligations		297,712		16,291		347		313,656		242,016		7,789		—		249,805
Residential mortgage-backed securities		2,536,999		70,222		531		2,606,690		1,910,909		20,268		7,020		1,924,157
Commercial mortgage-backed securities		1,965,664		136,056		720		2,101,000		1,570,765		19,880		4,178		1,586,467
Collateralized mortgage obligations		410,050		9,141		21		419,170		807,600		3,757		3,142		808,215
Corporate debt securities		8,000		185		2		8,183		8,000		21		33		7,988
	$	5,410,502	$	238,559	$	1,746	$	5,647,315	$	4,637,610	$	52,367	$	14,673	$	4,675,304

	September 30, 2020								December 31, 2019
			Gross		Gross				Gross		Gross
Securities Held to Maturity	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and government agency securities	$	—	$	—	$	—	$	—	$	50,000	$	3	$	—	$	50,003
Municipal obligations		630,894		49,348		17		680,225		641,019		27,146		69		668,096
Residential mortgage-backed securities		24,041		1,641		—		25,682		29,687		883		—		30,570
Commercial mortgage-backed securities		550,201		53,253		—		603,454		539,371		12,474		581		551,264
Collateralized mortgage obligations		203,825		4,502		—		208,327		307,932		3,597		458		311,071
	$	1,408,961	$	108,744	$	17	$	1,517,688	$	1,568,009	$	44,103	$	1,108	$	1,611,004

The following tables present the amortized cost and estimated fair value of debt securities available for sale and held to maturity at September 30, 2020 by contractual maturity. Actual maturities will differ from contractual maturities because of rights to call or repay obligations with or without penalties and scheduled and unscheduled principal payments on mortgage-backed securities and collateralized mortgage obligations.

The Company held no securities classified as trading at September 30, 2020 and December 31, 2019.

The following table presents the proceeds from, gross gain on, and gross losses on sales of securities during the nine months ended September 30, 2020 and 2019.

Securities with carrying values totaling $3.2 billion and $3.3 billion were pledged as collateral at September 30, 2020 and December 31, 2019 respectively, primarily to secure public deposits or securities sold under agreements to repurchase.

The Company’s policy is to invest only in securities of investment grade quality. These investments are largely limited to U.S. agency securities and municipal securities. Management has concluded, based on the long history of no credit losses, that the expectation of nonpayment of the held to maturity securities carried at amortized cost is zero for securities that are backed by the full faith and credit of and/or guaranteed by the U.S. government. As such, no allowance for credit losses has been recorded for these securities. The municipal portfolio is analyzed separately for allowance for credit loss in accordance with the applicable guidance for each portfolio as noted below.

Effective January 1, 2020, in conjunction with the adoption of CECL, and again at September 30, 2020, the Company evaluated credit impairment for individual securities available for sale whose fair value was below amortized cost with a more than inconsequential risk of default and where the Company had assessed the decline in fair value significant enough to suggest a credit event occurred. There were no securities that met the criteria of a credit loss event and therefore, no allowance for credit loss was recorded for either period. The fair value and gross unrealized losses for securities classified as available for sale with unrealized losses for the periods indicated follow.

Available for Sale
September 30, 2020	Losses < 12 months				Losses 12 months or >				Total
(in thousands)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. Treasury and government agency securities	$	44,039	$	125	$	—	$	—	$	44,039	$	125
Municipal obligations		26,010		347		—		—		26,010		347
Residential mortgage-backed securities		229,662		529		367		2		230,029		531
Commercial mortgage-backed securities		252,858		720		—		—		252,858		720
Collateralized mortgage obligations		3,300		21		—		—		3,300		21
Corporate debt securities		3,498		2		—		—		3,498		2
	$	559,367	$	1,744	$	367	$	2	$	559,734	$	1,746

Available for Sale
December 31, 2019	Losses < 12 months				Losses 12 months or >				Total
			Gross				Gross					Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government agency securities	$	28,235		300	$	—	$	—	$	28,235	$	300
Municipal obligations		—		—		—		—		—		—
Residential mortgage-backed securities		420,066		5,042		399,787		1,978		819,853		7,020
Commercial mortgage-backed securities		458,855		3,971		14,896		207		473,751		4,178
Collateralized mortgage obligations		89,689		1,315		184,389		1,827		274,078		3,142
Corporate debt securities		1,467		33		—		—		1,467		33
	$	998,312	$	10,661	$	599,072	$	4,012	$	1,597,384	$	14,673

Effective January 1, 2020 and in conjunction with the adoption of CECL, and again as of September 30, 2020, the Company evaluated its held to maturity municipal obligation portfolio for credit loss using probability of default and loss given default models. The models were run using a long-term average probability of default migration and with a probability weighting of Moody’s economic forecasts. The economic forecasts were largely weighted to a baseline scenario with some weight given to other scenarios. The September 30, 2020 forecast was further stressed by running a more severe probability of default migration. The resulting credit loss was negligible for both periods and no allowance for credit loss was recorded. The fair value and gross unrealized losses for securities classified as held to maturity with unrealized losses for the periods indicated follow.

Held to Maturity
September 30, 2020	Losses < 12 months				Losses 12 months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government agency securities	$	—	$	—	$	—	$	—	$	—	$	—
Municipal obligations		523		2		2,890		15		3,413		17
Residential mortgage-backed securities		—		—		—		—		—		—
Commercial mortgage-backed securities		222		—		—		—		222		—
Collateralized mortgage obligations		—		—		—		—		—		—
	$	745	$	2	$	2,890	$	15	$	3,635	$	17

Held to Maturity
December 31, 2019	Losses < 12 months				Losses 12 months or >				Total
			Gross		Gross							Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government agency securities	$	—	$	—	$	—	$	—	$	—	$	—
Municipal obligations		4,735		38		3,143		31		7,878		69
Residential mortgage-backed securities		—		—		—		—		—		—
Commercial mortgage-backed securities		28,426		581		—		—		28,426		581
Collateralized mortgage obligations		—		—		49,110		458		49,110		458
	$	33,161	$	619	$	52,253	$	489	$	85,414	$	1,108

As of September 30, 2020 the Company had 40 securities with market values below their cost basis. Unrealized losses in both portfolios relate primarily to changes in interest rates on fixed rate debt securities since the respective purchase dates. In all cases, the indicated impairment on these debt securities would be recovered no later than the security’s maturity date or possibly earlier if the market price for the security increases with a reduction in the yield required by the market. None of the unrealized losses relate to the marketability of the securities or the issuers’ abilities to meet contractual obligations. The Company had adequate liquidity as of September 30, 2020 and December 31, 2019 and did not intend to nor believe that it would be required to sell these securities before recovery of the indicated impairment. The unrealized losses on these securities were determined to be non-credit related as of December 31, 2019 and as noted above, no allowance for credit losses was recorded as of January 1, 2020 or September 30, 2020.