Derivative Instruments and Hedging Activities (Details)	Mar. 31, 2012 Open Natural Gas Derivative Positions [Member] 2012 [Member] Fixed-Price Swaps [Member] USD ($) MMBTU GJ	Mar. 31, 2012 Open Natural Gas Derivative Positions [Member] 2012 [Member] Fixed-Price Swaps [Member] CAD	Mar. 31, 2012 Open Natural Gas Derivative Positions [Member] 2012 [Member] Collars [Member] USD ($) GJ MMBTU	Mar. 31, 2012 Open Natural Gas Derivative Positions [Member] 2012 [Member] Collars [Member] CAD	Mar. 31, 2012 Open Natural Gas Derivative Positions [Member] 2013 [Member] Fixed-Price Swaps [Member] USD ($) MMBTU	Mar. 31, 2012 Open Natural Gas Derivative Positions [Member] 2013 [Member] Collars [Member] USD ($) MMBTU	Mar. 31, 2012 Open Natural Gas Derivative Positions [Member] 2014 [Member] Fixed-Price Swaps [Member] USD ($) MMBTU	Mar. 31, 2012 Open Crude Oil Derivative Positions [Member] 2012 [Member] Fixed-Price Swaps [Member] USD ($) MMBbls	Mar. 31, 2012 Open Crude Oil Derivative Positions [Member] 2012 [Member] Collars [Member] USD ($) MMBbls	Mar. 31, 2012 Open Crude Oil Derivative Positions [Member] 2013 [Member] Fixed-Price Swaps [Member] USD ($) MMBbls	Mar. 31, 2012 Open Crude Oil Derivative Positions [Member] 2013 [Member] Collars [Member] USD ($) MMBbls	Mar. 31, 2012 Open Crude Oil Derivative Positions [Member] 2014 [Member] Fixed-Price Swaps [Member] USD ($) MMBbls
Commodity Derivative Instruments
Mbbls	35,508,000	35,508,000	16,500,000	16,500,000	10,095,000	6,825,000	1,295,000	2,996,000	9,122,000	1,972,000	5,701,000	76,000
GJ	33,000,000	33,000,000	5,500,000	5,500,000
Weighted Average Fixed Price	$ 6.22	6.61			$ 6.74		$ 6.72	$ 73.73		$ 74.29		$ 74.50
Weighted Average Floor Price			5.54	6.50		5.35			76.80		82.84
Weighted Average Ceiling price			$ 7.30	7.27		$ 6.67			$ 101.68		$ 111.63