Derivative Activities - Schedule of Additional Information Related to Master Netting Arrangements with Derivative Counterparties (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 336,633	$ 404,118
Gross Amounts Offset in the Balance Sheet	(3,458)	(755)
Net Amounts of Assets Presented in the Balance Sheet	333,175	403,363
Gross Amounts of Recognized (Liabilities)	(3,862)	(755)
Gross Amounts Offset in the Balance Sheet	3,458	755
Net Amounts of (Liabilities) Presented in the Balance Sheet	(404)	0
Natural Gas | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	213,837	198,740
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	213,837	198,740
Natural Gas | Collars
Derivative [Line Items]
Gross Amounts of Recognized Assets	19,657	57,460
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	19,657	57,460
Natural Gas | Basis Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	1,875	2,442
Gross Amounts Offset in the Balance Sheet	(3,458)	(755)
Net Amounts of Assets Presented in the Balance Sheet	(1,583)	1,687
Gross Amounts of Recognized (Liabilities)	(3,862)	(755)
Gross Amounts Offset in the Balance Sheet	3,458	755
Net Amounts of (Liabilities) Presented in the Balance Sheet	(404)	0
Crude Oil | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets		128,578
Gross Amounts Offset in the Balance Sheet		0
Net Amounts of Assets Presented in the Balance Sheet		128,578
Crude Oil | Sold Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	66,494
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Assets Presented in the Balance Sheet	66,494
Crude Oil | Re-purchased Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	1,287
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Assets Presented in the Balance Sheet	1,287
Commodity Contract NGLs (C3 - Propane) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	13,933	14,727
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	13,933	14,727
Commodity Contract NGLs (NC4 - Normal Butane) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	6,004
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Assets Presented in the Balance Sheet	6,004
Commodity Contract NGLs (C5 - Natural Gasoline) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	13,546	2,171
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	$ 13,546	$ 2,171