Supplementary Information on Oil and Gas Operations—Unaudited - Proved Reserves (Details)	12 Months Ended
	Dec. 31, 2014 MBbls	Dec. 31, 2013 MBbls	Dec. 31, 2012 MBbls
Proved Developed and Undeveloped Reserves [Abstract]
Proved undeveloped reserve		5,088,000	5,817,000
Oil
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves beginning balance	3,031,000	(156,000)	1,395,000
Revisions of previous estimates (1)	(37,000)	434,000	195,000
Extensions, discoveries and other additions	475,000	1,833,000	647,000
Sale of reserves in place	0	(34,000)	(81,000)
Production	(229,000)		(521,000)
Proved reserves as of December 31, 2012	(803,000)	(681,000)	(1,635,000)
Proved reserves ending balance	2,437,000	3,031,000	(156,000)
Proved developed reserves	2,089,000	2,709,000	1,225,000
Proved undeveloped reserve	348,000	322,000	410,000
Natural Gas Liquids
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves, ending balance	28,430,000	804,000	15,111,000
Revisions of previous estimates (1)	2,894,000	6,099,000	(1,952,000)
Extensions, discoveries and other additions	49,990,000	1,915,000	14,572,000
Sale of reserves in place	0	0	0
Production	(334,000)		(3,365,000)
Proved reserves as of December 31, 2012	(7,482,000)	(4,754,000)	(24,366,000)
Proved reserves, ending balance	73,498,000	28,430,000	804,000
Proved undeveloped reserve	42,584,000	23,173,000	20,608,000
Proved developed reserves	30,914,000	5,257,000	3,758,000
Natural Gas
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves beginning balance	250,109,000	38,383,000	241,926,000
Revisions of previous estimates (1)	9,976,000	30,429,000	(56,780,000)
Extensions, discoveries and other additions	82,364,000	22,274,000	46,390,000
Sale of reserves in place	0	(15,000)	(15,806,000)
Production	(2,396,000)		(27,466,000)
Proved reserves as of December 31, 2012	(31,028,000)	(29,226,000)	(188,264,000)
Proved reserves ending balance	309,025,000	250,109,000	38,383,000
Proved developed reserves	182,567,000	163,728,000	140,307,000
Proved undeveloped reserve	126,458,000	86,381,000	47,957,000
Oil and Natural Gas Reserves
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves, ending balance	296,723,000	38,247,000	265,407,000
Revisions of previous estimates (1)	12,650,000	39,132,000	(57,561,000)
Extensions, discoveries and other additions	135,205,000	35,187,000	64,844,000
Sale of reserves in place	0	(218,000)	(16,292,000)
Production	(4,105,000)		(33,957,000)
Proved reserves as of December 31, 2012	(43,325,000)	(38,066,000)	(222,441,000)
Proved reserves, ending balance	397,148,000	296,723,000	38,247,000
Proved undeveloped reserve	237,688,000	203,152,000	168,265,000
Proved developed reserves	159,460,000	93,571,000	54,176,000