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Summary of Significant Accounting Policies (Concentration Risk) (Details) - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Oxy | Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage	28.00%	20.00%	19.00%
Oxy | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	26.00%	14.00%
Devon | Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage		15.00%	21.00%

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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.

+ References

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