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Commitments and Contingencies - MarkWest Environmental Proceeding (Details) - MarkWest Liberty Midstream Pipeline Launcher/Receiver Site - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended
--- | --- | ---
Apr. 30, 2018 | Mar. 31, 2018
Cash | Pending Litigation |  |
Loss Contingencies [Line Items] |  |
Damages sought |  | $ 0.6
Cash | Subsequent Event | Settled Litigation |  |
Loss Contingencies [Line Items] |  |
Damages sought | $ 0.6 |
Other Liabilities | Pending Litigation |  |
Loss Contingencies [Line Items] |  |
Damages sought |  | $ 2.4
Other Liabilities | Subsequent Event | Settled Litigation |  |
Loss Contingencies [Line Items] |  |
Damages sought | $ 2.4 |

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