Derivative Instruments And Hedging Activities Notional Contracts by Derivative Type (Details)	9 Months Ended
	Sep. 30, 2017 MMBTU bbl
Economic Hedges [Member] | Commodity Contract [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	918,000
Economic Hedges [Member] | Commodity Contract [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	918,000
Economic Hedges [Member] | WTI Crude Oil [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	700,000
Economic Hedges [Member] | WTI Crude Oil [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	700,000
Economic Hedges [Member] | Natural Gas Liquids [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	2,577,000
Economic Hedges [Member] | Natural Gas Liquids [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	2,577,000
Economic Hedges [Member] | Natural Gas - long [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	2,400,000
Economic Hedges [Member] | Natural Gas - long [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	2,400,000
Economic Hedges [Member] | Natural Gas - Short [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	2,400,000
Economic Hedges [Member] | Natural Gas - Short [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	2,400,000
Economic Hedges [Member] | NYMEX WTI short [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	1,870,000
Economic Hedges [Member] | NYMEX WTI short [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	955,000
Economic Hedges [Member] | NYMEX WTI short [Member] | Maturing in Year Three [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	915,000
Economic Hedges [Member] | Forward Contracts [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	715,000
Economic Hedges [Member] | Forward Contracts [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	705,000
Economic Hedges [Member] | Forward Contracts [Member] | Maturing in Year Three [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	10,000
Price Risk Derivative [Member] | Natural Gas - long [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	9,600,000
Price Risk Derivative [Member] | Natural Gas - long [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	2,400,000
Price Risk Derivative [Member] | Natural Gas - long [Member] | Maturing in Year Two [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	1,800,000
Price Risk Derivative [Member] | Natural Gas - long [Member] | Maturing in Year Five [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	1,800,000
Price Risk Derivative [Member] | Natural Gas - long [Member] | Maturing in Year Four [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	1,800,000
Price Risk Derivative [Member] | Natural Gas - long [Member] | Maturing in Year Three [Member]
Economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	1,800,000
Price Risk Derivative [Member] | Other Contract [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	150,000
Price Risk Derivative [Member] | Other Contract [Member] | Maturing in Next Twelve Months [Member]
Economic hedges by derivative type [Line Items]
Price Risk Fair Value Hedge Derivative, at Fair Value, Net | bbl	150,000