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, 2020 MMBTU $ / MMBTU $ / bbl $ / units bbl
Sell (Short) Contracts | Designated as hedges under accounting rules | Futures | Crude Oil
Derivative [Line Items]
Contract volumes (1,000 bbls) | bbl	444
Weighted average contract price per bbl (in dollars per barrel)	43.39
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	458
Weighted average contract price per bbl (in dollars per barrel)	42.32
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	2.54
Contract volumes (1,000 MMBTU) | MMBTU	101
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)	0.25
Contract volumes (1,000 MMBTU) | MMBTU	136
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	41
Weighted average premium received (in dollars per barrel)	1.01
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	160
Weighted average contract price per bbl (in dollars per barrel)	39.08
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	2.53
Contract volumes (1,000 MMBTU) | MMBTU	205
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	23
Weighted average premium received (in dollars per barrel)	1.21