Derivative Activities - Derivative Volumes Hedged and Average Hedge Prices (Detail)	Sep. 30, 2017 MMBTU / d bbl / d $ / MMBTU $ / bbl $ / gal
2017 Commodity Contract | Swaps | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	878,370	[1]
Weighted Average Hedge Price | $ / MMBTU	3.21	[1]
2017 Commodity Contract | Swaps | Crude Oil
Derivative [Line Items]
Volume Hedged | bbl / d	9,511	[1]
Weighted Average Hedge Price | $ / bbl	56.03	[1]
2017 Commodity Contract | Swaps | NGLs (C2-Ethane)
Derivative [Line Items]
Volume Hedged | bbl / d	3,000
Weighted Average Hedge Price | $ / gal	0.27
2017 Commodity Contract | Swaps | NGLs (C3-Propane)
Derivative [Line Items]
Volume Hedged | bbl / d	17,576
Weighted Average Hedge Price | $ / gal	0.61
2017 Commodity Contract | Swaps | NGLs (NC4-Normal Butane)
Derivative [Line Items]
Volume Hedged | bbl / d	9,000
Weighted Average Hedge Price | $ / gal	0.76
2017 Commodity Contract | Swaps | NGLs (C5-Natural Gasoline)
Derivative [Line Items]
Volume Hedged | bbl / d	6,416
Weighted Average Hedge Price | $ / gal	1.08
2017 Commodity Contract | Collars | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	122,609	[1]
Weighted Average Floor Price | $ / MMBTU	3.45	[1]
Weighted Average Cap Price | $ / MMBTU	4.11	[1]
2017 Commodity Contract | Puts | Purchased | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	185,870	[1]
Weighted Average Hedge Price | $ / MMBTU	3.50	[1],[2]
2017 Commodity Contract | Calls | Sold | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	17,935
Weighted Average Hedge Price | $ / MMBTU	3.75	[3]
2018 Commodity Contract | Swaps | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	477,534
Weighted Average Hedge Price | $ / MMBTU	3.22
2018 Commodity Contract | Swaps | Crude Oil
Derivative [Line Items]
Volume Hedged | bbl / d	6,000
Weighted Average Hedge Price | $ / bbl	52.96
2018 Commodity Contract | Swaps | NGLs (C2-Ethane)
Derivative [Line Items]
Volume Hedged | bbl / d	250
Weighted Average Hedge Price | $ / gal	0.29
2018 Commodity Contract | Swaps | NGLs (C3-Propane)
Derivative [Line Items]
Volume Hedged | bbl / d	8,935
Weighted Average Hedge Price | $ / gal	0.66
2018 Commodity Contract | Swaps | NGLs (NC4-Normal Butane)
Derivative [Line Items]
Volume Hedged | bbl / d	4,558
Weighted Average Hedge Price | $ / gal	0.81
2018 Commodity Contract | Swaps | NGLs (C5-Natural Gasoline)
Derivative [Line Items]
Volume Hedged | bbl / d	4,027
Weighted Average Hedge Price | $ / gal	1.17
2018 Commodity Contract | Collars | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	60,000
Weighted Average Floor Price | $ / MMBTU	3.40
Weighted Average Cap Price | $ / MMBTU	3.76
January-March 2019 Commodity Contract | Swaps | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	50,000
Weighted Average Hedge Price | $ / MMBTU	3.01
April-December 2018 Commodity Contract | Swaptions | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	320,000	[4]
Weighted Average Hedge Price | $ / MMBTU	3.04	[4]
2019 Commodity Contract | Swaps | Crude Oil
Derivative [Line Items]
Volume Hedged | bbl / d	1,000
Weighted Average Hedge Price | $ / bbl	51.50
2019 Commodity Contract | Swaptions | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	60,000	[4]
Weighted Average Hedge Price | $ / MMBTU	3.00	[4]

[1] Includes derivative instruments assumed in connection with the MRD Merger.

[2] Weighted average deferred premium is ($0.32).

[3] Weighted average deferred premium is $0.31.

[4] Contains a combined derivative instrument consisting of a fixed price swap and a sold option to extend or double the volume. For April through December of 2018, we have swaps in place for 160,000 Mmbtu per day on which the counterparty can elect to double the volume at a weighted average price of $3.02. We also have swaps in place for 160,000 Mmbtu per day on which the counterparty can elect to extend the contract through December 2019 at a weighted average price of $3.07. In 2019, if the counterparty elects to double the volume, we would have additional swaps covering 60,000 Mmbtu per day at a weighted average price of $3.00.