Oil and Gas Reserve Information - Unaudited - Proved reserves (Details)	12 Months Ended
	Dec. 31, 2013 MBbls	Dec. 31, 2012 MBbls	Dec. 31, 2011 MBbls
Oil [Member]
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves beginning balance	1,655,000	1,395,000	1,623,000
Revisions of previous estimates	(123,000)	215,000	(294,000)
Extensions, discoveries and other additions	434,000	647,000	595,000
Purchase of producing properties	1,833,000	(81,000)	43,000
Sale of reserves in place	(34,000)
Production	(681,000)	(521,000)	(572,000)
Proved reserves ending balance	3,084,000	1,655,000	1,395,000
Proved developed reserves	2,709,000	1,225,000	1,160,000
Proved undeveloped reserve	375,000	430,000	235,000
Natural Gas Liquids [Member]
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves, ending balance	25,360,000	15,111,000	8,373,000
Revisions of previous estimates	520,000	(958,000)	308,000
Extensions, discoveries and other additions	6,099,000	14,572,000	8,627,000
Purchase of producing properties	1,915,000	0	91,000
Sale of reserves in place	0
Production	(4,754,000)	(3,365,000)	(2,288,000)
Proved reserves, ending balance	29,140,000	25,360,000	15,111,000
Proved developed reserves	5,967,000	4,752,000	4,040,000
Proved undeveloped reserve	23,173,000	20,608,000	11,071,000
Natural Gas [Member]
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves beginning balance	192,968,000	241,926,000	174,566,000
Revisions of previous estimates	37,738,000	(52,076,000)	8,418,000
Extensions, discoveries and other additions	30,429,000	46,390,000	82,113,000
Purchase of producing properties	22,274,000	(15,806,000)	1,292,000
Sale of reserves in place	(15,000)
Production	(29,226,000)	(27,466,000)	(24,463,000)
Proved reserves ending balance	254,168,000	192,968,000	241,926,000
Proved developed reserves	163,728,000	140,307,000	143,441,000
Proved undeveloped reserve	90,440,000	52,661,000	98,485,000
Oil and Natural Gas Reserves [Member]
Proved Developed and Undeveloped Reserves [Abstract]
Proved reserves, ending balance	228,258,000	265,407,000	192,677,000
Revisions of previous estimates	37,518,000	(51,744,000)	6,962,000
Extensions, discoveries and other additions	39,132,000	64,844,000	94,310,000
Purchase of producing properties	35,187,000	(16,292,000)	1,641,000
Sale of reserves in place	(218,000)
Production	(38,066,000)	(33,957,000)	(30,183,000)
Proved reserves, ending balance	301,811,000	228,258,000	265,407,000
Proved developed reserves	98,659,000	59,993,000	103,935,000
Proved undeveloped reserve	203,152,000	168,265,000	161,472,000