Derivative Instrument - Schedule of Company's Open Commodity Contracts (Detail) - Fixed price/basis swaps	9 Months Ended
	Sep. 30, 2018 BTU $ / MBbls $ / BTU bbl
Oil fixed price swaps
Derivative Instruments [Line Items]
Volume (Bbl) | bbl	8,373,350
Weighted average price (usd per bbl) | $ / MBbls	60.08
Oil fixed price swaps | 2018
Derivative Instruments [Line Items]
Volume (Bbl) | bbl	1,233,180
Weighted average price (usd per bbl) | $ / MBbls	57.09
Oil fixed price swaps | 2019
Derivative Instruments [Line Items]
Volume (Bbl) | bbl	5,540,670
Weighted average price (usd per bbl) | $ / MBbls	59.86
Oil fixed price swaps | 2020
Derivative Instruments [Line Items]
Volume (Bbl) | bbl	1,599,500
Weighted average price (usd per bbl) | $ / MBbls	63.14
Natural gas fixed price swaps
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	49,529,000
Weighted average price (usd per bbl) | $ / BTU	2.81
Natural gas fixed price swaps | 2018
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	8,004,000
Weighted average price (usd per bbl) | $ / BTU	2.94
Natural gas fixed price swaps | 2019
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	29,200,000
Weighted average price (usd per bbl) | $ / BTU	2.86
Natural gas fixed price swaps | 2020
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	12,325,000
Weighted average price (usd per bbl) | $ / BTU	2.63
Natural gas basis swaps
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	30,140,000
Weighted average price (usd per bbl) | $ / BTU	0.58
Natural gas basis swaps | 2018
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	4,600,000
Weighted average price (usd per bbl) | $ / BTU	0.54
Natural gas basis swaps | 2019
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	21,900,000
Weighted average price (usd per bbl) | $ / BTU	0.58
Natural gas basis swaps | 2020
Derivative Instruments [Line Items]
Volume (MMBtu) | BTU	3,640,000
Weighted average price (usd per bbl) | $ / BTU	0.62