The amortized cost, gross unrealized gains and losses, and estimated fair value of securities classified as available for sale and held to maturity at March 31, 2020 and December 31, 2019 as follow. Amortized cost of securities does not include accrued interest which is reflected in the accrued interest line item on the Consolidated Balance Sheets totaling $22.8 million and $23.9 million at March 31, 2020 and December 31, 2019, respectively.

Securities Available for Sale
(in thousands)	March 31, 2020								December 31, 2019
			Gross		Gross				Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and government agency securities	$	107,750		1,676		223	$	109,203	$	98,320	$	652	$	300	$	98,672
Municipal obligations		241,050		8,643		—		249,693		242,016		7,789		—		249,805
Residential mortgage-backed securities		2,061,777		62,764		10		2,124,531		1,910,909		20,268		7,020		1,924,157
Commercial mortgage-backed securities		1,648,643		94,268		105		1,742,806		1,570,765		19,880		4,178		1,586,467
Collateralized mortgage obligations		641,855		17,712		—		659,567		807,600		3,757		3,142		808,215
Corporate debt securities		8,000		218		22		8,196		8,000		21		33		7,988
	$	4,709,075	$	185,281	$	360	$	4,893,996	$	4,637,610	$	52,367	$	14,673	$	4,675,304

	March 31, 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		627,185		29,093		20		656,258		641,019		27,146		69		668,096
Residential mortgage-backed securities		28,236		1,309		—		29,545		29,687		883		—		30,570
Commercial mortgage-backed securities		538,865		41,782		—		580,647		539,371		12,474		581		551,264
Collateralized mortgage obligations		286,208		9,921		2		296,127		307,932		3,597		458		311,071
	$	1,480,494	$	82,105	$	22	$	1,562,577	$	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 March 31, 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 March 31, 2020 and December 31, 2019.

During the three months ended March 31, 2020, proceeds from the sales of securities totaled $124.1 million, with gross gains of $1.1 million and gross losses of $1.0 million. There were no sales of securities during the three months ended March 31, 2019.

Securities with carrying values totaling $4.8 billion and $3.3 billion at March 31, 2020 and December 31, 2019, respectively, were pledged as collateral, primarily to secure public deposits or securities sold under agreements to repurchase and, at March 31, 2020, to provide enhanced liquidity through additional borrowing capacity at the Federal Reserve.

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 March 31, 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
March 31, 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	$	7,807	$	223	$	—	$	—	$	7,807	$	223
Municipal obligations		—		—		—		—		—		—
Residential mortgage-backed securities		714		5		1,688		5		2,402		10
Commercial mortgage-backed securities		25,196		105		—		—		25,196		105
Collateralized mortgage obligations		—		—		—		—		—		—
Corporate debt securities		778		22		—		—		778		22
	$	34,495	$	355	$	1,688	$	5	$	36,183	$	360

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 March 31, 2020, the Company evaluated its 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 forecast. The economic forecast was largely weighted to a baseline forecast with some weight given to downside scenarios for both periods. The March 31, 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
March 31, 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		—		—		2,894		20		2,894		20
Residential mortgage-backed securities		—		—		—		—		—		—
Commercial mortgage-backed securities		—		—		—		—		—		—
Collateralized mortgage obligations		—		—		1,287		2		1,287		2
	$	—	$	—	$	4,181	$	22	$	4,181	$	22

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

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 March 31, 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 March 31, 2020.