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Summary of Significant Accounting Policies (Concentration Risk) (Details) - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	35.00%	26.00%
Oxy | Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage	36.00%	28.00%	15.00%
Oxy | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	35.00%	26.00%
Devon | Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage			20.00%

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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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+ References

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