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Summary of Significant Accounting Policies - Schedule of Gas Derivative Contracts Volume and Prices (Detail)
Jun. 30, 2018
MMBTU
$ / MMBTU
Gas Contracts, in MMBTU | Swap Contracts for Q3  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 5,400,000
Gas Contracts, in MMBTU | Swap Contracts for Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 5,400,000
Gas Contracts, in MMBTU | Swap Contracts for Q3 and Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 10,800,000
Gas Contracts, in MMBTU | Swap Contracts for 2019  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 4,200,000
Gas Contracts, in MMBTU | Swap Contracts  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 15,000,000
Gas Contracts, in MMBTU | Collar Contract One for Q3  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 2,700,000
Gas Contracts, in MMBTU | Collar Contract One for Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 2,700,000
Gas Contracts, in MMBTU | Collar Contract One for Q3 and Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 5,400,000
Gas Contracts, in MMBTU | Collar Contract One for 2019  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 5,400,000
Gas Contracts, in MMBTU | Collar Contract One  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 10,800,000
Gas Contracts, in MMBTU | Collar Contract Two for Q3  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 2,700,000
Gas Contracts, in MMBTU | Collar Contract Two for Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 2,700,000
Gas Contracts, in MMBTU | Collar Contract Two for Q3 and Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 5,400,000
Gas Contracts, in MMBTU | Collar Contract Two for 2019  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 5,400,000
Gas Contracts, in MMBTU | Collar Contract Two  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 10,800,000
Gas Contracts, Price per MMBTU | Swap Contracts for Q3  
Derivative [Line Items]  
Price per MMBtu in usd 3.00
Gas Contracts, Price per MMBTU | Swap Contracts for Q4  
Derivative [Line Items]  
Price per MMBtu in usd 3.00
Gas Contracts, Price per MMBTU | Swap Contracts for Q3 and Q4  
Derivative [Line Items]  
Price per MMBtu in usd 3.00
Gas Contracts, Price per MMBTU | Swap Contracts for 2019  
Derivative [Line Items]  
Price per MMBtu in usd 3.00
Gas Contracts, Price per MMBTU | Swap Contracts  
Derivative [Line Items]  
Price per MMBtu in usd 3.00
Gas Contracts, Price per MMBTU | Collar Contract One for Q3  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.30
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract One for Q4  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.30
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract One for Q3 and Q4  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.30
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract One for 2019  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.30
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract One  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.30
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract Two for Q3  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.50
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract Two for Q4  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.50
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract Two for Q3 and Q4  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.50
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract Two for 2019  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.50
Floor, price per MMBTU 2.50
Gas Contracts, Price per MMBTU | Collar Contract Two  
Derivative [Line Items]  
Ceiling, price per MMBTU 3.50
Floor, price per MMBTU 2.50