Derivative Activities - Derivative Volumes Hedged and Average Hedge Prices (Parenthetical) (Detail) - 2017 Commodity Contract - Natural Gas	Jun. 30, 2017 $ / MMBTU
Puts \| Purchased
Derivative [Line Items]
Weighted average deferred premium - purchases	(0.32)
Calls \| Sold
Derivative [Line Items]
Weighted average deferred premium - sales	0.27

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.

No definition available.

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