Additional Financial Statement Information - Non-Affiliated Purchasers Accounting for 10% or More of Commodity Sales (Details) - Sales - Customer Concentration Risk	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Crude Oil \| Shell
Concentration Risk [Line Items]
Concentration risk, percentage	22.00%	22.00%	22.00%
Crude Oil \| BP
Concentration Risk [Line Items]
Concentration risk, percentage	18.00%	31.00%	15.00%
Total Crude Oil, NGL & Natural Gas Sales \| Shell
Concentration Risk [Line Items]
Concentration risk, percentage	15.00%	14.00%	13.00%
Total Crude Oil, NGL & Natural Gas Sales \| BP
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%	17.00%	10.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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