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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The proportionate share of interest (percent) in a jointly owned utility plant.

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-Name Accounting Standards Codification
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-Section S99
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Amount of transactions with related party during the financial reporting period.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Nov. 05, 2015
Predecessor \| Affiliated Entity
Related Party Transaction [Line Items]
Revenue from related parties			$ 1.4
Black Warrior Methane (BWM)
Related Party Transaction [Line Items]
Proportionate consolidation method, ownership percentage					50.00%
Black Warrior Transmission (BWT)
Related Party Transaction [Line Items]
Equity method investment, ownership percentage					50.00%
Allocated Expenses to Joint Venture \| Successor \| Corporate Joint Venture
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.1	$ 0.3		$ 0.8
Allocated Expenses to Joint Venture \| Predecessor \| Corporate Joint Venture
Related Party Transaction [Line Items]
Expenses from transactions with related party			$ 0.3