Derivatives (Schedule of Outstanding Derivatives Entered Into to Hedge Inventory or Fixed Price Purchase Commitments) (Details) bbl in Thousands, MMBTU in Thousands	6 Months Ended
	Jun. 30, 2021 MMBTU $ / bbl $ / MMBTU bbl
Designated as hedges under accounting rules | Sell (Short) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls) | bbl	92
Weighted average contract price | $ / bbl	70.71
Designated as hedges under accounting rules | Buy (Long) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls) | bbl	0
Weighted average contract price | $ / bbl	0
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls) | bbl	204
Weighted average contract price | $ / bbl	70.75
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Future | Natural Gas
Derivative [Line Items]
Contract volume (MMBTU) | MMBTU	15
Weighted average contract price | $ / MMBTU	3.55
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Options | Crude Oil
Derivative [Line Items]
Contract volumes (bbls) | bbl	8
Weighted average premium received/paid | $ / bbl	5.59
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls) | bbl	10
Weighted average contract price | $ / bbl	72.66
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Future | Natural Gas
Derivative [Line Items]
Contract volume (MMBTU) | MMBTU	15
Weighted average contract price | $ / MMBTU	3.14
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Options | Crude Oil
Derivative [Line Items]
Contract volumes (bbls) | bbl	0
Weighted average premium received/paid | $ / bbl	0