Supplemental Oil and Gas Reserve Information (Details)	12 Months Ended
	Dec. 31, 2012 Boe		Dec. 31, 2011 Boe		Dec. 31, 2010 Boe		Dec. 31, 2009 Boe
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Net (BOE)	75,357,000		64,349,000		51,065,000		33,637,000
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates (BOE)	(6,615,000)		(2,007,000)		2,282,000
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions (BOE)	20,443,000		20,881,000		23,193,000
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place (BOE)	3,504,000				349,000
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place (BOE)	(725,000)		(156,000)		(2,937,000)
Proved Developed and Undeveloped Reserves, Production (BOE)	(5,599,000)		(5,434,000)		(5,459,000)
Proved Developed Reserves (BOE)	43,354,000		39,264,000		34,472,000
Oil
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, net (at beginning)	49,536,000	[1]	37,815,000	[1]	20,953,000	[1]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	(5,498,000)	[1]	(1,802,000)	[1]	1,511,000	[1]
Extensions and discoveries	16,676,000	[1]	17,570,000	[1]	18,969,000	[1]
Purchases of minerals-in-place	2,474,000	[1]			317,000	[1]
Sales of minerals-in-place	(633,000)	[1]	(45,000)	[1]	(268,000)	[1]
Production	(4,254,000)	[1]	(4,002,000)	[1]	(3,667,000)	[1]
Proved developed and undeveloped reserves, net (at end)	58,301,000	[1]	49,536,000	[1]	37,815,000	[1]
Proved Developed Reserves (Volume)	32,685,000	[1]	28,962,000	[1]	24,570,000	[1]
Gas
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, net (at beginning)	88,876,000		79,497,000		76,103,000
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	(6,699,000)		(1,227,000)		4,628,000
Extensions and discoveries	22,604,000		19,864,000		25,343,000
Purchases of minerals-in-place	6,182,000				190,000
Sales of minerals-in-place	(555,000)		(664,000)		(16,017,000)
Production	(8,072,000)		(8,594,000)		(10,750,000)
Proved developed and undeveloped reserves, net (at end)	102,336,000		88,876,000		79,497,000
Proved Developed Reserves (Volume)	64,013,000		61,811,000		59,409,000
Performance Estimate [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates (BOE)	4,339
Pricing Estimate [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates (BOE)	2,276

[1] Includes natural gas liquids.