Subsequent Events - Additional Information (Detail) - Fixed price swaps	1 Months Ended	9 Months Ended
	Nov. 13, 2018 BTU $ / BTU	Sep. 30, 2018 BTU $ / BTU
Natural gas fixed price swaps
Subsequent Event [Line Items]
Fixed price swap | BTU		49,529,000
Weighted average price (usd per bbl) | $ / BTU		2.81
Natural gas fixed price swaps | January 2019 to December 2019
Subsequent Event [Line Items]
Fixed price swap | BTU		29,200,000
Weighted average price (usd per bbl) | $ / BTU		2.86
Subsequent event | NGL price | October 2018 to December 2019
Subsequent Event [Line Items]
Fixed price swap | BTU	2,500
Subsequent event | Natural Gas Liquids Commodity Contracts Member [Domain] | October 2018 to December 2019
Subsequent Event [Line Items]
Weighted average price (usd per bbl) | $ / BTU	34.03
Subsequent event | Natural gas fixed price swaps | January 2019 to December 2019
Subsequent Event [Line Items]
Fixed price swap | BTU	20,000
Weighted average price (usd per bbl) | $ / BTU	2.93