Quarterly report pursuant to Section 13 or 15(d)

Property Acquisition and Operating Leases (Narrative) (Details)

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Property Acquisition and Operating Leases (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended 1 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2012
Northern portion of Midland Basin [Member]
acre
Feb. 28, 2012
Northern portion of Midland Basin [Member]
Borden County Acreage Purchase [Member]
acre
Jul. 05, 2012
Property Acquisitions [Member]
Southern Reagan County, Texas [Member]
acre
Sep. 30, 2012
Property Acquisitions [Member]
Northern portion of Midland Basin [Member]
acre
Sep. 30, 2012
Horizontal Drilling Rig [Member]
Sep. 30, 2012
Horizontal Drilling Rig [Member]
Feb. 28, 2011
Horizontal Drilling Rig [Member]
Permian Basin [Member]
Sep. 30, 2012
Horizontal Drilling Rig [Member]
Early Termination Provision if Sub Lessor is Found [Member]
Property                    
Contracted drilling rig, term (in years)                 2 years  
Operating lease payments             $ 2,327 $ 4,283    
Operating Leases, Future Minimum Payments Due                    
Lease payments in 2012             6,611 6,611   4,434
Lease payments in 2012 in remainder of fiscal year             2,328 2,328   1,689
Lease payments in 2013             9,234 9,234   5,475
Lease payments in 2014             2,619 2,619   1,350
Acquired acreage, undeveloped, gross (in acreas)     8,375 16,020 2,319          
Acquired acreage, undeveloped, net (in acres)     5,940 14,470 1,762 1,024        
Business Acquisition, Cost of Acquired Entity, Purchase Price     4,133 15,000 12,000 717        
Unevaluated property balance $ 45,672 $ 2,603