Derivatives (Schedule of Outstanding Derivatives Entered Into to Hedge Inventory or Fixed Price Purchase Commitments) (Details) gal in Thousands, bbl in Thousands, MMBTU in Thousands	3 Months Ended
	Mar. 31, 2019 MMBTU $ / bbl $ / MMBTU $ / gal gal bbl
Designated as hedges under accounting rules | Sell (Short) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	56
Weighted average contract price | $ / bbl	57.25
Designated as hedges under accounting rules | Buy (Long) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	0
Weighted average contract price | $ / bbl	0.00
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	336
Weighted average contract price | $ / bbl	57.90
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Future | Natural Gas
Derivative [Line Items]
Contract volume (MMBTU) | MMBTU	136
Weighted average contract price | $ / MMBTU	2.74
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Future | NYM RBOB Gas Futures
Derivative [Line Items]
Contract volumes (bbls/gallon) | gal	4
Weighted average contract price | $ / gal	1.80
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Future | Fuel Oil Futures
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	184
Weighted average contract price | $ / bbl	63.14
Not qualifying or not designated as hedges under accounting rules | Sell (Short) Contracts | Options | Crude Oil
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	35
Weighted average premium received | $ / bbl	1.21
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Future | Crude Oil
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	133
Weighted average contract price | $ / bbl	59.24
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Future | Natural Gas
Derivative [Line Items]
Contract volume (MMBTU) | MMBTU	606
Weighted average contract price | $ / MMBTU	2.80
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Future | NYM RBOB Gas Futures
Derivative [Line Items]
Contract volumes (bbls/gallon) | gal	4
Weighted average contract price | $ / gal	1.81
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Future | Fuel Oil Futures
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	100
Weighted average contract price | $ / bbl	62.97
Not qualifying or not designated as hedges under accounting rules | Buy (Long) Contracts | Options | Crude Oil
Derivative [Line Items]
Contract volumes (bbls/gallon) | bbl	10
Weighted average premium received | $ / bbl	0.25