Derivatives (Outstanding Derivatives Entered Into to Hedge Inventory or Fixed Price Purchase Commitments) (Details) bbl in Thousands, MMBTU in Thousands	12 Months Ended
Dec. 31, 2019 MMBTU $ / bbl $ / MMBTU $ / units bbl
Sell (Short) Contracts \| Designated as hedges under accounting rules \| Futures \| Crude Oil
Derivative [Line Items]
Contract volumes (1,000 bbls) \| bbl	19
Weighted average contract price per bbl (in dollars per barrel)	58.57
Sell (Short) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Futures \| Crude Oil
Derivative [Line Items]
Contract volumes (1,000 bbls) \| bbl	79
Weighted average contract price per bbl (in dollars per barrel)	60.25
Sell (Short) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Futures \| Natural Gas
Derivative [Line Items]
Weighted average contract price per bbl (in dollars per barrel) \| $ / MMBTU	2.27
Contract volumes (1,000 MMBTU) \| MMBTU	92
Sell (Short) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Swap \| Natural Gas
Derivative [Line Items]
Weighted average contract price per bbl (in dollars per barrel)	0.38
Contract volumes (1,000 MMBTU) \| MMBTU	503
Sell (Short) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Options \| Crude Oil
Derivative [Line Items]
Contract volumes (1,000 bbls) \| bbl	40
Weighted average premium received (in dollars per barrel)	1.03
Buy (Long) Contracts \| Designated as hedges under accounting rules \| Futures \| Crude Oil
Derivative [Line Items]
Contract volumes (1,000 bbls) \| bbl	0
Weighted average contract price per bbl (in dollars per barrel)	0
Buy (Long) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Futures \| Crude Oil
Derivative [Line Items]
Contract volumes (1,000 bbls) \| bbl	80
Weighted average contract price per bbl (in dollars per barrel)	60.25
Buy (Long) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Futures \| Natural Gas
Derivative [Line Items]
Weighted average contract price per bbl (in dollars per barrel) \| $ / MMBTU	2.60
Contract volumes (1,000 MMBTU) \| MMBTU	576
Buy (Long) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Swap \| Natural Gas
Derivative [Line Items]
Weighted average contract price per bbl (in dollars per barrel) \| $ / units	0
Contract volumes (1,000 MMBTU) \| MMBTU	0
Buy (Long) Contracts \| Not qualifying or not designated as hedges under accounting rules \| Options \| Crude Oil
Derivative [Line Items]
Contract volumes (1,000 bbls) \| bbl	18
Weighted average premium received (in dollars per barrel)	0.66

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