Quarterly report pursuant to Section 13 or 15(d)

Property Disclosures and Operating Leases (Narrative) (Details)

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Property Disclosures and Operating Leases (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
 6 Months Ended 3 Months Ended 6 Months Ended 1 Months Ended 0 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Horizontal Drilling Rig [Member]
Jun. 30, 2013
Horizontal Drilling Rig [Member]
Dec. 31, 2012
Horizontal Drilling Rig [Member]
Jun. 30, 2013
Horizontal Drilling Rig [Member]
Early Termination Provision if Sub Lessor is Found [Member]
Apr. 30, 2012
Horizontal Drilling Rig One [Member]
Permian Basin [Member]
Aug. 01, 2013
Horizontal Drilling Rig Two [Member]
Permian Basin [Member]
Subsequent Event [Member]
Jun. 01, 2013
Southern Reagan County, Texas [Member]
bbl
Oil_well
acre
Property                  
Contracted drilling rig, term (in years)             2 years 1 year  
Operating lease payments     $ 2,280 $ 4,551          
Business Acquisitions                  
Gross acres acquired                 2,468
Net acres acquired                 2,186
Gross number of oil wells acquired                 7
Number of barrels of oil equivalent proved reserves acquired                 1,051,000
Purchase price (11,000) 0             (11,000)
Operating Leases, Future Minimum Payments Due                  
Lease payments in 2013         12,601 5,055      
Lease payments in 2013 in remainder of fiscal year     8,050 8,050          
Lease payments in 2014     $ 6,941 $ 6,941   $ 4,530