Derivative Activities - Derivative Volumes Hedged and Average Hedge Prices (Detail)	Sep. 30, 2018 MMBTU / d bbl / d $ / MMBTU $ / bbl $ / gal
2018 Commodity Contract | Swaps | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	1,193,370
Weighted Average Hedge Price | $ / MMBTU	2.96
2018 Commodity Contract | Swaps | Crude Oil
Derivative [Line Items]
Volume Hedged	8,500
Weighted Average Hedge Price | $ / bbl	53.20
2018 Commodity Contract | Swaps | NGLs (C3-Propane)
Derivative [Line Items]
Volume Hedged	11,668
Weighted Average Hedge Price | $ / gal	0.74
2018 Commodity Contract | Swaps | NGLs (NC4-Normal Butane)
Derivative [Line Items]
Volume Hedged	5,500
Weighted Average Hedge Price | $ / gal	0.91
2018 Commodity Contract | Swaps | NGLs (C5-Natural Gasoline)
Derivative [Line Items]
Volume Hedged	5,402
Weighted Average Hedge Price | $ / gal	1.24
2018 Commodity Contract | Calls | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	70,000
Weighted Average Hedge Price | $ / MMBTU	3.10	[1]
2018 Commodity Contract | Swaptions | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	160,000
Weighted Average Hedge Price | $ / MMBTU	3.07	[2]
2018 Commodity Contract | Collars | NGLs (C3-Propane)
Derivative [Line Items]
Volume Hedged	5,000
2018 Commodity Contract | Collars | NGLs (C3-Propane) | Minimum
Derivative [Line Items]
Weighted Average Hedge Price | $ / bbl	0.95
2018 Commodity Contract | Collars | NGLs (C3-Propane) | Maximum
Derivative [Line Items]
Weighted Average Hedge Price | $ / bbl	1.04
2019 Commodity Contract | Swaps | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	594,589
Weighted Average Hedge Price | $ / MMBTU	2.82
2019 Commodity Contract | Swaps | Crude Oil
Derivative [Line Items]
Volume Hedged	7,000
Weighted Average Hedge Price | $ / bbl	55.26
2019 Commodity Contract | Swaps | NGLs (C5-Natural Gasoline)
Derivative [Line Items]
Volume Hedged	2,178
Weighted Average Hedge Price | $ / gal	1.42
2019 Commodity Contract | Swaptions | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	298,014
Weighted Average Hedge Price | $ / MMBTU	2.86	[2]
2019 Commodity Contract | Collars | Crude Oil
Derivative [Line Items]
Volume Hedged	1,000
2019 Commodity Contract | Collars | Crude Oil | Minimum
Derivative [Line Items]
Weighted Average Hedge Price | $ / bbl	63.00
2019 Commodity Contract | Collars | Crude Oil | Maximum
Derivative [Line Items]
Weighted Average Hedge Price | $ / bbl	73.03
2020 Commodity Contract | Swaps | Crude Oil
Derivative [Line Items]
Volume Hedged	1,500
Weighted Average Hedge Price | $ / bbl	60.63
2020 Commodity Contract | Swaptions | Natural Gas
Derivative [Line Items]
Volume Hedged | MMBTU / d	10,000
Weighted Average Hedge Price | $ / MMBTU	2.75	[2]
January – March 2019 Commodity Contract | Swaps | NGLs (NC4-Normal Butane)
Derivative [Line Items]
Volume Hedged	2,250
Weighted Average Hedge Price | $ / gal	1.22
January – March 2019 Commodity Contract | Collars | NGLs (C3-Propane)
Derivative [Line Items]
Volume Hedged	6,500
January – March 2019 Commodity Contract | Collars | NGLs (C3-Propane) | Minimum
Derivative [Line Items]
Weighted Average Hedge Price | $ / bbl	0.92
January – March 2019 Commodity Contract | Collars | NGLs (C3-Propane) | Maximum
Derivative [Line Items]
Weighted Average Hedge Price | $ / bbl	1.02
January – June 2019 Commodity Contract | Swaps | NGLs (C3-Propane)
Derivative [Line Items]
Volume Hedged	7,500
Weighted Average Hedge Price | $ / gal	0.92

[1] Weighted average deferred premium of $0.16.

[2] Contains a combined derivative instrument consisting of a fixed price swap and a sold option to extend or double the volume. For October through December of 2018, we 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. We have swaps in place for 2019 for 185,000 Mmbtu/day on which the counterparty can elect to double the volume at a weighted average price of $2.89. We also have swaps in place for 2019 for 150,000 Mmbtu per day on which the counterparty can elect to extend the contract through December 2020 at a weighted average price of $2.81. For 2020, we have swaps in place for 10,000 Mmbtu/day on which the counterparty can elect to double the volume at a weighted average price of $2.75.