Summary of Significant Accounting Policies Credit Risk (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Concentration Risk, Percentage	63.00%	66.00%	49.00%
Occidental Energy Marketing [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage		21.00%	16.00%
Plains Marketing LP [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage		17.00%	12.00%
Valero Marketing And Supply Company [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	30.00%	18.00%
Phillips66 [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	12.00%