Annual report pursuant to Section 13 and 15(d)

Acquisitions (Purchase Price Allocation For Acquisition Of Properties) (Details)

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Acquisitions (Purchase Price Allocation For Acquisition Of Properties) (Details) (USD $)
 12 Months Ended
Dec. 31, 2011
May 11, 2011
Yellow Rose Properties [Member]
    
Business Acquisition [Line Items]    
Oil and natural gas properties and equipment $ 396,902,000 [1]  
Asset retirement obligations-non-current (382,000)  
Long-term liability (2,143,000)  
Total cash paid 394,377,000  
Business acquisition unproved properties excluded from full cost pool and amortization base 85,700,000 84,700,000
Increase in capitalized interest for proved properties 4,500,000  
Decrease due to reclassifications to unproved properties 3,500,000  
Fairway Properties [Member]
    
Business Acquisition [Line Items]    
Oil and natural gas properties and equipment 50,682,000  
Asset retirement obligations-non-current (7,812,000)  
Total cash paid 42,870,000  
Matterhorn/Virgo Properties [Member]
    
Business Acquisition [Line Items]    
Oil and natural gas properties and equipment 121,301,000  
Asset retirement obligations-non-current (6,289,000)  
Total cash paid 115,012,000  
Tahoe/Droshky Properties [Member]
    
Business Acquisition [Line Items]    
Oil and natural gas properties and equipment 134,189,000  
Asset retirement obligations-non-current (17,956,000)  
Total cash paid $ 116,233,000  
[1] At the acquisition date, $84.7 million was recorded as unproved properties. During 2011, this amount was increased by $4.5 million due to capitalized interest and decreased by $3.5 million due to reclassifications to proved properties resulting in $85.7 million in unproved properties as of December 31, 2011 for the Yellow Rose Properties. Amounts recorded as unproved properties are excluded from the full cost pool and amortization base.