3. Revenues

Our revenues are derived primarily from the sale of natural gas and electricity to customers, including affiliates. Revenue is measured based upon the quantity of gas or power delivered at prices contained or referenced in the customer's contract, and excludes any sales incentives (e.g. rebates) and amounts collected on behalf of third parties (e.g. sales tax).

Our revenues also include asset optimization activities. Asset optimization activities consist primarily of purchases and sales of gas that meet the definition of trading activities per FASB ASC Topic 815, Derivatives and Hedging. They are therefore excluded from the scope of FASB ASC Topic 606, Revenue from Contracts with Customers.

Revenues for electricity and natural gas sales are recognized under the accrual method when our performance obligation to a customer is satisfied, which is the point in time when the product is delivered and control of the product passes to the customer. Electricity and natural gas products may be sold as fixed-price or variable-price products. The typical length of a contract to provide electricity and/or natural gas is twelve months. Customers are billed and typically pay at least monthly, based on usage. Electricity and natural gas sales that have been delivered but not billed by period end are estimated and recorded as accrued unbilled revenues based on estimates of customer usage since the date of the last meter read provided by the utility. Volume estimates are based on forecasted volumes and estimated residential and commercial customer usage. Unbilled revenues are calculated by multiplying these volume estimates by the applicable rate by customer class (residential or commercial). Estimated amounts are adjusted when actual usage is known and billed.

The following table discloses revenue by primary geographical market, customer type, and customer credit risk profile (in thousands). The table also includes a reconciliation of the disaggregated revenue to revenue by reportable segment (in thousands).



	Reportable Segments
	Three Months Ended March 31, 2020									Three Months Ended March 31, 2019
	Retail Electricity			Retail Natural Gas			Total Reportable Segments			Retail Electricity			Retail Natural Gas			Total Reportable Segments


Primary markets (a)
New England	$	46,593		$	7,054		$	53,647		$	76,234		$	8,528		$	84,762
Mid-Atlantic	45,842			15,804			61,646			66,811			21,369			88,180
Midwest	14,989			13,607			28,596			22,107			20,489			42,596
Southwest	14,344			8,127			22,471			16,940			7,676			24,616
	$	121,768		$	44,592		$	166,360		$	182,092		$	58,062		$	240,154

Customer type
Commercial	$	40,015		$	15,517		$	55,532		$	67,235		$	19,867		$	87,102
Residential	93,228			33,363			126,591			124,768			41,095			165,863
Unbilled revenue (b)	(11,475		)	(4,288		)	(15,763		)	(9,911		)	(2,900		)	(12,811		)
	$	121,768		$	44,592		$	166,360		$	182,092		$	58,062		$	240,154

Customer credit risk
POR	$	84,913		$	23,037		$	107,950		$	128,937		$	28,979		$	157,916
Non-POR	36,855			21,555			58,410			53,155			29,083			82,238
	$	121,768		$	44,592		$	166,360		$	182,092		$	58,062		$	240,154

(a) The primary markets include the following states:


•	New England - Connecticut, Maine, Massachusetts, New Hampshire;


•	Mid-Atlantic - Delaware, Maryland (including the District of Colombia), New Jersey, New York and Pennsylvania;


•	Midwest - Illinois, Indiana, Michigan and Ohio; and


•	Southwest - Arizona, California, Colorado, Florida, Nevada, and Texas.

(b) Unbilled revenue is recorded in total until it is actualized, at which time it is categorized between commercial and residential customers.

We record gross receipts taxes on a gross basis in retail revenues and retail cost of revenues. During the three months ended March 31, 2020 and 2019, our retail revenues included gross receipts taxes of $0.3 million and $0.4 million, respectively, and our retail cost of revenues included gross receipts taxes of $1.7 million and $2.7 million, respectively.