Derivative Instruments and Hedging Activities (Details)	Jun. 30, 2011 USD ($)	Jun. 30, 2011 Open Crude Oil Derivative Positions [Member] 2011 [Member] Fixed-Price Swaps [Member] USD ($)	Jun. 30, 2011 Open Crude Oil Derivative Positions [Member] 2011 [Member] Collars [Member] USD ($)	Jun. 30, 2011 Open Crude Oil Derivative Positions [Member] 2012 [Member] Fixed-Price Swaps [Member] USD ($)	Jun. 30, 2011 Open Crude Oil Derivative Positions [Member] 2012 [Member] Collars [Member] USD ($)	Jun. 30, 2011 Open Crude Oil Derivative Positions [Member] 2013 [Member] Fixed-Price Swaps [Member] USD ($)	Jun. 30, 2011 Open Crude Oil Derivative Positions [Member] 2013 [Member] Collars [Member] USD ($)	Jun. 30, 2011 Open Crude Oil Derivative Positions [Member] 2014 [Member] Fixed-Price Swaps [Member] USD ($)	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2011 [Member] Fixed-Price Swaps [Member] USD ($)	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2011 [Member] Fixed-Price Swaps [Member] CAD	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2011 [Member] Collars [Member] USD ($)	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2011 [Member] Collars [Member] CAD	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2012 [Member] Fixed-Price Swaps [Member] USD ($)	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2012 [Member] Fixed-Price Swaps [Member] CAD	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2012 [Member] Collars [Member] USD ($)	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2012 [Member] Collars [Member] CAD	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2013 [Member] Fixed-Price Swaps [Member] USD ($)	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2013 [Member] Collars [Member] USD ($)	Jun. 30, 2011 Open Natural Gas Derivative Positions [Member] 2014 [Member] Fixed-Price Swaps [Member] USD ($)
Commodity Derivative Instruments [Abstract]
Mbbls		2,641,000	14,996,000	3,786,000	9,142,000	1,860,000	2,416,000	76,000	35,884,000	35,884,000	4,600,000	4,600,000	41,544,000	41,544,000	21,960,000	21,960,000	7,665,000	6,825,000	755,000
GJ									25,760,000	25,760,000	1,840,000	1,840,000	43,920,000	43,920,000	7,320,000	7,320,000
Weighted Average Fixed Price		$ 74.17		$ 72.26		$ 74.38		$ 74.50	$ 5.96	6.26			$ 6.3	6.61			$ 6.83		$ 7.23
Weighted Average Floor Price			69.18		69.30		78.02				5.00	6.50			5.54	6.50		5.35
Weighted Average Ceiling price	$ 98.56		$ 96.79		$ 98.11		$ 103.06				$ 8.85	7.10			$ 7.30	7.27		$ 6.67