Derivatives (Cash Flow Hedges Outstanding) (Details)	12 Months Ended
	Dec. 31, 2012 Unit bbl
Not Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'13 - Dec'13 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (in Bbl/day)	1,000
Weighted Average Fixed Price for Swaps	90.63
Not Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'13 - Dec'13 [Member] | Start [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Jan'13
Not Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'13 - Dec'13 [Member] | End [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Dec'13
Not Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'14 - Dec'14 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (in Bbl/day)	1,000
Weighted Average Fixed Price for Swaps	90.60
Not Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'14 - Dec'14 [Member] | Start [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Jan'14
Not Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'14 - Dec'14 [Member] | End [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Dec'14
Not Designated as Hedging Instrument [Member] | Swap [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (MMBtu/day)	20,000
Weighted Average Fixed Price for Swaps	3.94
Not Designated as Hedging Instrument [Member] | Swap [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member] | Start [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Jan'13
Not Designated as Hedging Instrument [Member] | Swap [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member] | End [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Dec'13
Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'13 - Dec'13 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (in Bbl/day)	5,500
Weighted Average Fixed Price for Swaps	99.71
Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'13 - Dec'13 [Member] | Start [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Jan'13
Designated as Hedging Instrument [Member] | Swap [Member] | WTI - NYMEX [Member] | Crude Oil [Member] | Jan'13 - Dec'13 [Member] | End [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Dec'13
Designated as Hedging Instrument [Member] | Swap [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (MMBtu/day)	60,000
Weighted Average Fixed Price for Swaps	3.56
Designated as Hedging Instrument [Member] | Swap [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member] | Start [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Jan'13
Designated as Hedging Instrument [Member] | Swap [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member] | End [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Dec'13
Designated as Hedging Instrument [Member] | Collar [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (MMBtu/day)	20,000
Designated as Hedging Instrument [Member] | Collar [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member] | Start [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Jan'13
Weighted Average Fixed Price for Swaps	3.25
Designated as Hedging Instrument [Member] | Collar [Member] | IF - NYMEX (HH) [Member] | Natural Gas [Member] | Jan'13 - Dec'13 [Member] | End [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Commodity Derivatives Term	Dec'13
Weighted Average Fixed Price for Swaps	3.72