Derivative Instruments and Hedging Activities (Derivative Positions and Settlements) (Details) (Not Designated as Hedging Instrument [Member], Commodity Contract [Member])	Mar. 31, 2013
Crude Oil [Member] | Derivative Average Floor Price per Instrument of 93 Point 35 Dollars and Average Ceiling Price per Instrument of 93 Point 35 Dollars [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount (in Volumes per Month)	30,000
Fixed-Price Swap	93.35
Crude Oil [Member] | Average Floor Price per Instrument of $70 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount (in Volumes per Month)	30,000
Put/Call Price	70.00
Natural gas [Member] | Fixed-Price Swap per Instrument of 3 Point 52 Dollars [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount (in Volumes per Month)	91,000
Fixed-Price Swap	3.52
Natural gas [Member] | Average Floor Price per Instrument of $3.00 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount (in Volumes per Month)	91,000
Put/Call Price	3.00
Natural gas [Member] | Average Ceiling Price per Instrument of $4.75 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount (in Volumes per Month)	38,000
Put/Call Price	4.75
Subsequent Event [Member] | Crude Oil [Member] | Derivative Average Floor Price per Instrument of 101 Point 30 Dollars and Average Ceiling Price per Instrument of 101 Point 30 Dollars [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount (in Volumes per Month)	40,000
Fixed-Price Swap	101.30