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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- Definition

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

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Amount of transactions with related party during the financial reporting period.

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-Topic 850
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Nov. 05, 2015
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 \| Corporate Joint Venture
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.7	$ 0.1	$ 1.5	$ 0.8