Number of miles the pipeline is operated.

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The cash outflow associated with additional investments in or advances to an entity in which the reporting entity shares control of the entity with another party or group. Excludes initial investment.

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Percentage of interest held in third party assets by our joint venture.

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Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Equity Method Investments (Details) $ in Thousands		3 Months Ended		9 Months Ended
Equity Method Investments (Details) $ in Thousands	Feb. 06, 2017	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2016 mi
Investments in unconsolidated affiliates
Balance at beginning of period				$ 303,302
Additional investments				91,419
Equity in net income of unconsolidated affiliates		$ 10,706	$ 7,033	27,832	$ 12,887
Distributions from unconsolidated affiliates				(29,660)	$ (10,120)
Balance at end of period		392,893		392,893
MarkWest
Investments in unconsolidated affiliates
Balance at beginning of period				236,174
Additional investments				91,419
Equity in net income of unconsolidated affiliates				19,486
Distributions from unconsolidated affiliates				(22,145)
Balance at end of period		324,934		324,934
Stonewall
Investments in unconsolidated affiliates
Balance at beginning of period				67,128
Equity in net income of unconsolidated affiliates				8,346
Distributions from unconsolidated affiliates				(7,515)
Balance at end of period		$ 67,959		$ 67,959
Appalachia Joint venture
Equity Method Investments
Ownership percentage	50.00%
Percentage of interest held by joint venture in third party fractionator in Ohio	33.33%
Appalachia Joint venture \| MarkWest
Equity Method Investments
Ownership percentage	50.00%	50.00%		50.00%
Stonewall Gas Gathering LLC
Equity Method Investments
Ownership percentage		15.00%		15.00%		15.00%
Number of miles \| mi						67