DISCLOSURES ABOUT OIL AND GAS PRODUCING ACTIVITIES (UNAUDITED): (Details)	0 Months Ended	12 Months Ended
	Dec. 31, 2010 bbl	Dec. 31, 2012 bbl	Dec. 31, 2011 bbl
Changes in quantities of proved oil, natural gas liquids and natural gas reserves
Extensions and discoveries		20,461
Revisions to previous estimates for pricing		(100)	336
Revisions to previous estimates		(6,938)
Number of locations that were moved from unproved to proved undeveloped		50
Wattenberg Field, Rocky Mountain Region
Changes in quantities of proved oil, natural gas liquids and natural gas reserves
Extensions and discoveries		17,380	12,117
Extensions and discoveries (as a percent)		85.00%
Oil (Bbl)
Changes in quantities of proved oil, natural gas liquids and natural gas reserves
Balance at the beginning of the period		28,216,000	22,379,000
Extensions and discoveries		12,016,000	7,182,000
Sales of mineral in place		(669,000)
Purchases of minerals in place	22,398,000
Production	(19,000)	(2,529,000)	(1,137,000)
Revisions to previous estimates		(3,768,000)	(208,000)
Balance at the end of the period	22,379,000	33,266,000	28,216,000
Proved developed reserves:	8,180,000	15,675,000	11,842,000
Proved undeveloped reserves:	14,199,000	17,591,000	16,374,000
Oil and gas commodity price (in dollars per Bbl/ MMBtu)		94.71	96.19
Increase in oil and gas commodity price (in dollars per Bbl)			16.76
Natural Gas (MMcf)
Changes in quantities of proved oil, natural gas liquids and natural gas reserves
Balance at the beginning of the period		92,982	62,884
Extensions and discoveries		50,667	29,608
Purchases of minerals in place	62,926
Production	(42)	(5,475)	(2,776)
Revisions to previous estimates		(19,626)	3,266
Balance at the end of the period	62,884	118,548	92,982
Proved developed reserves:	20,074	48,942	31,313
Proved undeveloped reserves:	42,810	69,606	61,669
Oil and gas commodity price (in dollars per Bbl/ MMBtu)		2.757	4.12