Supplemental Information on Oil and Gas Producing Activities (Unaudited) (Details 2)	12 Months Ended
Dec. 31, 2014 MMcfe	Dec. 31, 2013 MMcfe	Dec. 31, 2012 MMcfe
Proved developed and undeveloped reserves:
Balance at the beginning of the period	7,632,000	4,929,000	5,017,000
Revisions	(1,054,000)	(788,000)	222,000
Extensions, discoveries and other additions	6,444,000	3,682,000	1,951,000
Production	(368,000)	(191,000)	(87,000)
Purchase of reserves	29,000
Sale of reserves in place			(2,174,000)
Balance at the end of the period	12,683,000	7,632,000	4,929,000
Oil and Gas Reserves
Proved developed reserves	3,803,000us-gaap_ProvedDevelopedReservesBOE1	2,022,000us-gaap_ProvedDevelopedReservesBOE1	1,047,000us-gaap_ProvedDevelopedReservesBOE1
Proved undeveloped reserves	8,880,000us-gaap_ProvedUndevelopedReserveBOE1	5,610,000us-gaap_ProvedUndevelopedReserveBOE1	3,822,000us-gaap_ProvedUndevelopedReserveBOE1
Natural gas
Proved developed and undeveloped reserves:
Balance at the beginning of the period	6,753,000	3,694,000	3,931,000
Revisions	(1,025,000)	152,000	198,000
Extensions, discoveries and other additions	5,095,000	3,084,000	1,242,000
Production	(317,000)	(177,000)	(87,000)
Purchase of reserves	29,000
Sale of reserves in place			(1,590,000)
Balance at the end of the period	10,535,000	6,753,000	3,694,000
Oil and Gas Reserves
Proved developed reserves	3,285	1,818	828
Proved undeveloped reserves	7,250	4,936	2,866
NGLS
Proved developed and undeveloped reserves:
Balance at the beginning of the period	137,000	203,000	164,000
Revisions	(6,000)	(140,000)	4,000
Extensions, discoveries and other additions	206,000	76,000	115,000
Production	(7,000)	(2,000)
Sale of reserves in place			(80,000)
Balance at the end of the period	330,000	137,000	203,000
Oil and Gas Reserves
Proved developed reserves	80,000	33,000	36,000
Proved undeveloped reserves	250,000	105,000	167,000
Oil and condensate
Proved developed and undeveloped reserves:
Balance at the beginning of the period	10,000	3,000	17,000
Extensions, discoveries and other additions	19,000	7,000	3,000
Production	(1,000)
Sale of reserves in place			(17,000)
Balance at the end of the period	28,000	10,000	3,000
Oil and Gas Reserves
Proved developed reserves	6,000	2,000	1,000
Proved undeveloped reserves	22,000	8,000	2,000

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Additions to proved reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reservoirs of proved reserves in old fields.