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Summary of Significant Accounting Policies - Schedule of Gas Derivative Contracts Volume and Prices (Detail)
Sep. 30, 2018
MMBTU
bbl
$ / bbl
$ / MMBTU
Natural Gas Contracts, in MMBTU | Swap Contracts for Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 5,400,000
Average price per MMBtu in usd 3.00
Natural Gas Contracts, in MMBTU | Swap Contracts for 2019  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 4,200,000
Average price per MMBtu in usd 3.00
Natural Gas Contracts, in MMBTU | Swap Contracts  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 9,600,000
Average price per MMBtu in usd 3.00
Natural Gas Contracts, in MMBTU | Collar Contracts for Q4  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 6,300,000
Ceiling, Average price per MMBTU 3.40
Floor, Average price per MMBTU 2.50
Natural Gas Contracts, in MMBTU | Swap Contracts for 2019  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 13,200,000
Ceiling, Average price per MMBTU 3.40
Floor, Average price per MMBTU 2.50
Natural Gas Contracts, in MMBTU | Collar Contracts  
Derivative [Line Items]  
Volume, MMBTU | MMBTU 19,500,000
Ceiling, Average price per MMBTU 3.40
Floor, Average price per MMBTU 2.50
Crude Oil Contracts, in Barrels | Collar Contracts for Q4  
Derivative [Line Items]  
Volume, MMBTU | bbl 315,000
Ceiling, Average price per MMBTU | $ / bbl 77.85
Floor, Average price per MMBTU | $ / bbl 55.00
Crude Oil Contracts, in Barrels | Swap Contracts for 2019  
Derivative [Line Items]  
Volume, MMBTU | bbl 855,000
Ceiling, Average price per MMBTU | $ / bbl 77.98
Floor, Average price per MMBTU | $ / bbl 55.00
Crude Oil Contracts, in Barrels | Collar Contracts  
Derivative [Line Items]  
Volume, MMBTU | bbl 1,170,000
Ceiling, Average price per MMBTU | $ / bbl 77.94
Floor, Average price per MMBTU | $ / bbl 55.00