Derivative Activities - Derivative Volumes Hedged and Average Hedge Prices (Parenthetical) (Detail) - Swaps	Sep. 30, 2019 MMBTU / d bbl / d bbl $ / MMBTU $ / bbl
2021 Commodity Contract | Counterparty Can Elect to Double The Volume | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	30,000
Weighted average price of hedge | $ / MMBTU	2.70
2021 Commodity Contract | Counterparty Can Elect to Double The Volume | Crude Oil
Derivative [Line Items]
Volume Hedged | bbl	1,000
Weighted average price of hedge | $ / bbl	55.00
2019 Commodity Contract | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	1,271,739
Weighted average price of hedge | $ / MMBTU	2.82
2019 Commodity Contract | Crude Oil
Derivative [Line Items]
Volume Hedged | bbl / d	9,168
Weighted average price of hedge | $ / bbl	56.11
2019 Commodity Contract | Counterparty Can Elect to Extend Contract | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	140,000
Weighted average price of hedge | $ / MMBTU	2.81
2020 Commodity Contract | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	674,208
Weighted average price of hedge | $ / MMBTU	2.64
2020 Commodity Contract | Crude Oil
Derivative [Line Items]
Volume Hedged | bbl / d	6,738
Weighted average price of hedge | $ / bbl	58.53
2020 Commodity Contract | Counterparty Can Elect to Double The Volume | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	110,000
Weighted average price of hedge | $ / MMBTU	2.78
2020 Commodity Contract | Counterparty Can Elect to Extend Contract | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	50,000
Weighted average price of hedge | $ / MMBTU	2.75
2020 Commodity Contract | Counterparty Can Elect to Extend Contract | Crude Oil
Derivative [Line Items]
Volume Hedged | bbl	1,000
Weighted average price of hedge | $ / bbl	57.00