Derivative Activities - Schedule of Additional Information Related to Master Netting Arrangements with Derivative Counterparties (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 25,013	$ 33,360
Gross Amounts Offset in the Balance Sheet	(9,016)	(19,706)
Net Amounts of Assets Presented in the Balance Sheet	15,997	13,654
Gross Amounts of Recognized (Liabilities)	(82,012)	(45,929)
Gross Amounts Offset in the Balance Sheet	9,016	19,706
Net Amounts of (Liabilities) Presented in the Balance Sheet	(72,996)	(26,223)
Natural gas | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	8,347	4,240
Gross Amounts Offset in the Balance Sheet		(1,218)
Net Amounts of Assets Presented in the Balance Sheet	8,347	3,022
Gross Amounts of Recognized (Liabilities)	(27,720)	(4,790)
Gross Amounts Offset in the Balance Sheet		1,218
Net Amounts of (Liabilities) Presented in the Balance Sheet	(27,720)	(3,572)
Natural gas | Collars
Derivative [Line Items]
Gross Amounts of Recognized Assets	7,328	16,057
Gross Amounts Offset in the Balance Sheet	(584)	(7,671)
Net Amounts of Assets Presented in the Balance Sheet	6,744	8,386
Gross Amounts of Recognized (Liabilities)	(26,738)	(13,345)
Gross Amounts Offset in the Balance Sheet	584	7,671
Net Amounts of (Liabilities) Presented in the Balance Sheet	(26,154)	(5,674)
Natural gas | Basis Swap
Derivative [Line Items]
Gross Amounts of Recognized Assets	3,123	7,686
Gross Amounts Offset in the Balance Sheet	(3,123)	(7,686)
Net Amounts of Assets Presented in the Balance Sheet
Gross Amounts of Recognized (Liabilities)	(6,762)	(3,756)
Gross Amounts Offset in the Balance Sheet	3,123	7,686
Net Amounts of (Liabilities) Presented in the Balance Sheet	(3,639)	3,930
Crude oil | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	1,179	3,567
Gross Amounts Offset in the Balance Sheet	(273)	(1,321)
Net Amounts of Assets Presented in the Balance Sheet	906	2,246
Gross Amounts of Recognized (Liabilities)	(10,027)	(4,711)
Gross Amounts Offset in the Balance Sheet	273	1,321
Net Amounts of (Liabilities) Presented in the Balance Sheet	(9,754)	(3,390)
Crude oil | Collars
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(972)	(398)
Gross Amounts Offset in the Balance Sheet
Net Amounts of (Liabilities) Presented in the Balance Sheet	(972)	(398)
Swap NGLs (Natural Gasoline) | C3 swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	1,877	826
Gross Amounts Offset in the Balance Sheet	(1,877)	(826)
Net Amounts of Assets Presented in the Balance Sheet
Gross Amounts of Recognized (Liabilities)	(9,692)	(18,172)
Gross Amounts Offset in the Balance Sheet	1,877	826
Net Amounts of (Liabilities) Presented in the Balance Sheet	(7,815)	(17,346)
Swap NGLs (Natural Gasoline) | C4 swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	3,159	863
Gross Amounts Offset in the Balance Sheet	(3,159)	(863)
Net Amounts of Assets Presented in the Balance Sheet
Gross Amounts of Recognized (Liabilities)		(757)
Gross Amounts Offset in the Balance Sheet	3,159	863
Net Amounts of (Liabilities) Presented in the Balance Sheet	3,159	106
Swap NGLs (Natural Gasoline) | C5 swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets		121
Gross Amounts Offset in the Balance Sheet		(121)
Net Amounts of Assets Presented in the Balance Sheet
Gross Amounts of Recognized (Liabilities)	(101)
Gross Amounts Offset in the Balance Sheet		121
Net Amounts of (Liabilities) Presented in the Balance Sheet	$ (101)	$ 121