Acquisition of Southwest Royalties, Inc. Limited Partnerships (Details) (Southwest Royalties, Inc., Limited partnerships, USD $)	0 Months Ended	1 Months Ended
	Mar. 14, 2012 partnership	Mar. 31, 2012 Boe
Southwest Royalties, Inc. | Limited partnerships
Acquisition
Number of limited partnerships acquired	24
Percentage of assets and liabilities acquired		100.00%
Aggregate merger consideration paid	$ 38,600,000
Upfront cash proceeds under VPP		44,400,000
Deferred future advances under VPP		4,700,000
Barrels of oil equivalents of future oil and gas production covered by a term overriding royalty interest conveyed to a third party under the terms of the VPP		725,000
Summary of preliminary estimated fair value of the assets acquired and liabilities assumed
Cash and cash equivalents	4,118,000
Oil and gas properties	41,098,000
Other non-current assets	210,000
Total assets acquired	45,426,000
Asset retirement obligations	(6,864,000)
Total liabilities assumed	(6,864,000)
Net assets acquired	$ 38,562,000