The majority of our revenue is derived from long-term, fee-based contracts with original terms of up to 25 years. We account for revenue in accordance with Topic 606, which we adopted on January 1, 2018, using the modified retrospective method. See Note 2 for further discussion of the adoption, including the impact on our unaudited condensed consolidated financial statements.

We recognize revenue earned from fee-based gathering, treating and processing services in gathering services and related fees. We also earn revenue in the Williston Basin reporting segment from the sale of physical natural gas purchased from our customers under certain percent-of-proceeds arrangements. Under Topic 606, these gathering fee contracts are presented net within cost of natural gas and NGLs. We sell natural gas that we retain from certain DFW Midstream customers to offset the power expenses of the electric-driven compression on the DFW Midstream system. We also sell condensate retained from our gathering services at Grand River. Revenues from the sale of natural gas and condensate are recognized in natural gas, NGLs and condensate sales; the associated expense is included in operation and maintenance expense. Certain customers reimburse us for costs we incur on their behalf. We record costs incurred and reimbursed by our customers on a gross basis, with the revenue component recognized in other revenues.

The transaction price in our contracts is primarily based on the volume of natural gas, crude oil or produced water transferred by our gathering systems to the customer’s agreed upon delivery point multiplied by the contractual rate. For contracts that include MVCs, variable consideration up to the MVC will be included in the transaction price. For contracts that do not include MVCs, we do not estimate variable consideration because the performance obligations are completed and settled on a daily basis. For contracts containing noncash consideration such as fuel received in-kind, we measure the transaction price at the point of sale when the volume, mix and market price of the commodities are known.

We have contracts with MVCs that are variable and constrained. Contracts with MVCs are reviewed on a quarterly basis and adjustments to those estimates are made during each respective reporting period, if necessary.

The transaction price is allocated if the contract contains more than one performance obligation such as contracts that include MVCs. The transaction price allocated is based on the MVC for the applicable measurement period.

Performance obligations. The majority of our contracts have a single performance obligation which is either to provide gathering services (an integrated service) or sell natural gas, NGLs and condensate, which are both satisfied when the related natural gas, crude oil and produced water are received and transferred to an agreed upon delivery point. We also have certain contracts with multiple performance obligations. They include an option for the customer to acquire additional services such as contracts containing MVCs. These performance obligations would also be satisfied when the related natural gas, crude oil and produced water are received and transferred to an agreed upon delivery point. In these instances, we allocate the contract’s transaction price to each performance obligation using our best estimate of the standalone selling price of each service in the contract.

Performance obligations for gathering services are generally satisfied over time. We utilize either an output method (i.e., measure of progress) for guaranteed, stand-ready service contracts or an asset / system delivery time estimate for non-guaranteed, as-available service contracts.

Performance obligations for the sale of natural gas, NGLs and condensate are satisfied at a point in time. There are no significant judgments for these transactions because the customer obtains control based on an agreed upon delivery point.

Certain of our gathering and/or processing agreements provide for monthly, annual or multi-year MVCs. Under these MVCs, our customers agree to ship and/or process a minimum volume of production on our gathering systems or to pay a minimum monetary amount over certain periods during the term of the MVC. A customer must make a shortfall payment to us at the end of the contracted measurement period if its actual throughput volumes are less than its MVC for that period. Certain customers are entitled to utilize shortfall payments to offset gathering fees in one or more subsequent contracted measurement periods to the extent that such customer's throughput volumes in a subsequent contracted measurement period exceed its MVC for that contracted measurement period.

We recognize customer obligations under their MVCs as revenue and contract assets when (i) we consider it remote that the customer will utilize shortfall payments to offset gathering or processing fees in excess of its MVCs in subsequent periods; (ii) the customer incurs a shortfall in a contract with no banking mechanism or claw back provision; (iii) the customer’s banking mechanism has expired; or (iv) it is remote that the customer will use its unexercised right.

Our services are typically billed on a monthly basis and we do not offer extended payment terms. We do not have contracts with financing components.

The following table presents estimated revenue expected to be recognized during the remainder of 2018 and over the remaining contract period related to performance obligations that are unsatisfied and are comprised of estimated MVC shortfall payments.

We applied the practical expedient in paragraph 606-10-50-14 of Topic 606 for certain arrangements that we consider optional purchases (i.e., there is no enforceable obligation for the customer to make purchases) and those amounts are excluded from the table.

	2018		2019		2020		2021		2022		Thereafter
	(In thousands)
Gathering services and related fees	$	84,164	$	127,743	$	122,429	$	102,777	$	83,648	$	174,825

Revenue by Category. In the following table, revenue is disaggregated by geographic area and major products and services. For more detailed information about reportable segments, see Note 4.

	Reportable Segments
	Three months ended September 30, 2018
	Utica Shale		Williston Basin		Piceance / DJ Basins		Barnett Shale		Marcellus Shale		Total reportable segments		All other segments			Total
	(In thousands)
Major products/services lines
Gathering services and related fees	$	7,974	$	18,020	$	36,743	$	18,318	$	7,150	$	88,205	$	(1,778	)	$	86,427
Natural gas, NGLs and condensate sales		—		7,953		3,650		789		—		12,392		21,625			34,017
Other revenues		—		3,037		2,072		1,913		—		7,022		13			7,035
Total	$	7,974	$	29,010	$	42,465	$	21,020	$	7,150	$	107,619	$	19,860		$	127,479

	Reportable Segments
	Nine months ended September 30, 2018
	Utica Shale		Williston Basin		Piceance / DJ Basins		Barnett Shale		Marcellus Shale		Total reportable segments		All other segments			Total
	(In thousands)
Major products/services lines
Gathering services and related fees	$	28,437	$	58,792	$	108,207	$	46,035	$	23,025	$	264,496	$	(4,123	)	$	260,373
Natural gas, NGLs and condensate sales		—		23,149		12,650		1,715		—		37,514		54,511			92,025
Other revenues		—		8,909		6,187		5,595		—		20,691		(107	)		20,584
Total	$	28,437	$	90,850	$	127,044	$	53,345	$	23,025	$	322,701	$	50,281		$	372,982

Contract balances. Contract assets relate to our rights to consideration for work completed but not billed at the reporting date and consist of the estimated MVC shortfall payments expected from our customers and unbilled activity associated with contributions in aid of construction. Contract assets are transferred to trade receivables when the rights become unconditional. The following table provides information about contract assets from contracts with customers:

As of September 30, 2018, receivables with customers totaled $70.8 million and contract assets totaled $11.3 million which were included in the accounts receivable caption on the unaudited condensed consolidated balance sheet. In addition, long-term contract assets of $6.0 million, which are excluded from the table above, were included in the other noncurrent assets caption on the unaudited condensed consolidated balance sheet.

Contract liabilities (deferred revenue) relate to the advance consideration received from customers primarily for contributions in aid of construction. We recognize contract liabilities under these arrangements in revenue over the contract period. For the three and nine months ended September 30, 2018, we recognized $2.8 million and $7.8 million of gathering services and related fees which was included in the contract liability balance as of the beginning of the period. See Note 9 for additional details.