Major Customers Major Customers (Sales of Purchased Oil and Gas (Details) - Sales of Purchased Oil and Gas [Member]	12 Months Ended
Dec. 31, 2019 Rate	Dec. 31, 2018 Rate	Dec. 31, 2017 Rate
Occidental Energy Marketing Inc.
Concentration Risk [Line Items]
Concentration risk percent	30.00%	34.00%	39.00%
Valero Marketing and Supply Company
Concentration Risk [Line Items]
Concentration risk percent	2.00%	9.00%	14.00%
BP Corporation North America [Member]
Concentration Risk [Line Items]
Concentration risk percent	5.00%	9.00%	11.00%
Exxon Mobil [Member]
Concentration Risk [Line Items]
Concentration risk percent	4.00%	5.00%	11.00%

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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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