Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS AND PRICE RISK MANAGEMENT (Details)

v2.4.0.8
DERIVATIVE INSTRUMENTS AND PRICE RISK MANAGEMENT (Details) (USD $)
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Total volumes of open contracts 6,900,000   6,900,000  
Weighted average price on open contracts 89.95   89.95  
Oil Swap 1 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     300,000  
Fixed Price (in dollars per barrel) 91.65   91.65  
Oil Swap 1 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 1 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 2 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     120,000  
Fixed Price (in dollars per barrel) 89.50   89.50  
Oil Swap 2 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 2 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Oil Swap 3 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     60,000  
Fixed Price (in dollars per barrel) 91.10   91.10  
Oil Swap 3 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 3 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Oil Swap 4 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     30,000  
Fixed Price (in dollars per barrel) 94.50   94.50  
Oil Swap 4 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 4 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Oil Swap 5 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     30,000  
Fixed Price (in dollars per barrel) 102.30   102.30  
Oil Swap 5 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 5 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Oil Swap 6 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     30,000  
Fixed Price (in dollars per barrel) 94.50   94.50  
Oil Swap 6 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 6 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Oil Swap 7 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     356,250  
Fixed Price (in dollars per barrel) 88.55   88.55  
Oil Swap 7 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 7 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 8 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     356,250  
Fixed Price (in dollars per barrel) 88.60   88.60  
Oil Swap 8 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 8 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 9 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     356,250  
Fixed Price (in dollars per barrel) 88.40   88.40  
Oil Swap 9 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 9 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 10 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     356,250  
Fixed Price (in dollars per barrel) 88.50   88.50  
Oil Swap 10 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 10 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 11 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     510,000  
Fixed Price (in dollars per barrel) 89.15   89.15  
Oil Swap 11 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 11 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2015  
Oil Swap 12 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     810,000  
Fixed Price (in dollars per barrel) 89.00   89.00  
Oil Swap 12 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil Swap 12 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2015  
Oil Swap 13 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     300,000  
Fixed Price (in dollars per barrel) 89.50   89.50  
Oil Swap 13 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 13 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2014  
Oil Swap 14 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     240,000  
Fixed Price (in dollars per barrel) 90.00   90.00  
Oil Swap 14 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 14 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2014  
Oil Swap 15 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     240,000  
Fixed Price (in dollars per barrel) 100.00   100.00  
Oil Swap 15 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 15 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2014  
Oil Swap 16 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     120,000  
Fixed Price (in dollars per barrel) 91.35   91.35  
Oil Swap 16 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 16 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 17 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     120,000  
Fixed Price (in dollars per barrel) 90.00   90.00  
Oil Swap 17 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 17 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 18 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     240,000  
Fixed Price (in dollars per barrel) 90.15   90.15  
Oil Swap 18 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 18 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 19 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     240,000  
Fixed Price (in dollars per barrel) 91.00   91.00  
Oil Swap 19 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 19 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 20 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     120,000  
Fixed Price (in dollars per barrel) 93.00   93.00  
Oil Swap 20 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil Swap 20 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 21 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     120,000  
Fixed Price (in dollars per barrel) 90.00   90.00  
Oil Swap 21 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jul. 01, 2014  
Oil Swap 21 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 22 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     120,000  
Fixed Price (in dollars per barrel) 90.00   90.00  
Oil Swap 22 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jul. 01, 2014  
Oil Swap 22 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 23 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     120,000  
Fixed Price (in dollars per barrel) 93.50   93.50  
Oil Swap 23 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jul. 01, 2014  
Oil Swap 23 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 24 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     30,000  
Fixed Price (in dollars per barrel) 90.58   90.58  
Oil Swap 24 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jul. 01, 2014  
Oil Swap 24 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Oil Swap 25 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     60,000  
Fixed Price (in dollars per barrel) 90.50   90.50  
Oil Swap 25 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 25 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2015  
Oil Swap 26 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     180,000  
Fixed Price (in dollars per barrel) 88.55   88.55  
Oil Swap 26 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 26 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2015  
Oil Swap 27 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     180,000  
Fixed Price (in dollars per barrel) 88.00   88.00  
Oil Swap 27 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 27 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2015  
Oil Swap 29 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     60,000  
Fixed Price (in dollars per barrel) 90.25   90.25  
Oil Swap 29 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 29 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2015  
Oil Swap 28 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     60,000  
Fixed Price (in dollars per barrel) 90.75   90.75  
Oil Swap 28 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 28 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jun. 30, 2015  
Oil Swap 30 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     360,000  
Fixed Price (in dollars per barrel) 89.00   89.00  
Oil Swap 30 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 30 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2015  
Oil Swap 31 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     360,000  
Fixed Price (in dollars per barrel) 89.02   89.02  
Oil Swap 31 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 31 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2015  
Oil Swap 32 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     180,000  
Fixed Price (in dollars per barrel) 89.00   89.00  
Oil Swap 32 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 32 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2015  
Oil Swap 33 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Oil (in barrels)     180,000  
Fixed Price (in dollars per barrel) 89.00   89.00  
Oil Swap 33 [Member] | Minimum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2015  
Oil Swap 33 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2015  
Collar 1 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     32,187  
Price minimum (in dollars per barrel) $ 90.00   $ 90.00  
Price maximum (in dollars per barrel) $ 103.50   $ 103.50  
Collar 1 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 2 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     28,481  
Price minimum (in dollars per barrel) $ 90.00   $ 90.00  
Price maximum (in dollars per barrel) $ 106.50   $ 106.50  
Collar 2 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 3 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     49,412  
Price minimum (in dollars per barrel) $ 90.00   $ 90.00  
Price maximum (in dollars per barrel) $ 110.00   $ 110.00  
Collar 3 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 4 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     39,737  
Price minimum (in dollars per barrel) $ 95.00   $ 95.00  
Price maximum (in dollars per barrel) $ 107.00   $ 107.00  
Collar 4 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 5 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     120,000  
Price minimum (in dollars per barrel) $ 95.00   $ 95.00  
Price maximum (in dollars per barrel) $ 110.70   $ 110.70  
Collar 5 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 6 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     170,047  
Price minimum (in dollars per barrel) $ 85.00   $ 85.00  
Price maximum (in dollars per barrel) $ 98.00   $ 98.00  
Collar 6 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 7 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     30,000  
Price minimum (in dollars per barrel) $ 90.25   $ 90.25  
Price maximum (in dollars per barrel) $ 97.95   $ 97.95  
Collar 7 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 8 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     48,000  
Price minimum (in dollars per barrel) $ 95.00   $ 95.00  
Price maximum (in dollars per barrel) $ 106.90   $ 106.90  
Collar 8 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 9 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Oct. 01, 2013  
Oil (in barrels)     15,000  
Price minimum (in dollars per barrel) $ 93.00   $ 93.00  
Price maximum (in dollars per barrel) $ 100.00   $ 100.00  
Collar 9 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2013  
Collar 10 [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Jan. 01, 2014  
Oil (in barrels)     240,000  
Price minimum (in dollars per barrel) $ 90.00   $ 90.00  
Price maximum (in dollars per barrel) $ 99.05   $ 99.05  
Collar 10 [Member] | Maximum [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Settlement Period     Dec. 31, 2014  
Not Designated as Hedging Instrument [Member]
       
Crude Oil Derivative Contracts Cash-flow Not Designated as Hedges [Abstract]        
Realized gain (loss) on price risk derivatives not designated as hedges $ (8,096,075) $ 1,701,296 $ (8,966,175) $ (4,729,186)
Unrealized gain (loss) on price risk derivatives not designated as hedges $ (29,353,161) $ (22,308,470) $ (27,254,147) $ 18,125,928