Derivative Activities - Schedule of Additional Information Related to Master Netting Arrangements with Derivative Counterparties (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 277,359	$ 404,118
Gross Amounts Offset in the Balance Sheet	(8,538)	(755)
Net Amounts of Assets Presented in the Balance Sheet	268,821	403,363
Gross Amounts of Recognized (Liabilities)	(8,663)	(755)
Gross Amounts Offset in the Balance Sheet	8,538	755
Net Amounts of (Liabilities) Presented in the Balance Sheet	(125)	0
Natural Gas | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	157,138	198,740
Gross Amounts Offset in the Balance Sheet	(1,119)	0
Net Amounts of Assets Presented in the Balance Sheet	156,019	198,740
Gross Amounts of Recognized (Liabilities)	(1,244)
Gross Amounts Offset in the Balance Sheet	1,119
Net Amounts of (Liabilities) Presented in the Balance Sheet	(125)
Natural Gas | Collars
Derivative [Line Items]
Gross Amounts of Recognized Assets	31,149	57,460
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	31,149	57,460
Natural Gas | Basis Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	7,240	2,442
Gross Amounts Offset in the Balance Sheet	(1,380)	(755)
Net Amounts of Assets Presented in the Balance Sheet	5,860	1,687
Gross Amounts of Recognized (Liabilities)	(1,380)	(755)
Gross Amounts Offset in the Balance Sheet	1,380	755
Net Amounts of (Liabilities) Presented in the Balance Sheet	0	0
Crude Oil | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	64,690	128,578
Gross Amounts Offset in the Balance Sheet	(2,731)	0
Net Amounts of Assets Presented in the Balance Sheet	61,959	128,578
Gross Amounts of Recognized (Liabilities)	(2,731)
Gross Amounts Offset in the Balance Sheet	2,731
Net Amounts of (Liabilities) Presented in the Balance Sheet	0
Commodity Contract NGLs (C3 - Propane) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	13,966	14,727
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	13,966	14,727
Commodity Contract NGLs (NC4 - Normal Butane) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	2,774
Gross Amounts Offset in the Balance Sheet	(5)
Net Amounts of Assets Presented in the Balance Sheet	2,769
Gross Amounts of Recognized (Liabilities)	(5)
Gross Amounts Offset in the Balance Sheet	5
Net Amounts of (Liabilities) Presented in the Balance Sheet	0
Commodity Contract NGLs (C5 - Natural Gasoline) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	402	2,171
Gross Amounts Offset in the Balance Sheet	(3,303)	0
Net Amounts of Assets Presented in the Balance Sheet	(2,901)	$ 2,171
Gross Amounts of Recognized (Liabilities)	(3,303)
Gross Amounts Offset in the Balance Sheet	3,303
Net Amounts of (Liabilities) Presented in the Balance Sheet	$ 0