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

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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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Related Party Transactions - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Black Warrior Methane (BWM)
Related Party Transaction [Line Items]
Proportionate consolidation method, ownership percentage	50.00%		50.00%
Black Warrior Transmission (BWT)
Related Party Transaction [Line Items]
Equity method investment, ownership percentage	50.00%		50.00%
Allocated Expenses to Joint Venture \| Corporate Joint Venture
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.6	$ 0.6	$ 1.9	$ 1.1