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Summary of Significant Accounting Policies (Concentration Risk) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%
Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%
Devon | Sales and Rental Income | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	21.00%	18.00%	15.00%
Devon | Accounts Receivable | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%
Oxy | Sales and Rental Income | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%
Oxy | Accounts Receivable | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	25.00%	14.00%
EOG | Sales and Rental Income | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage		15.00%	18.00%
Promatcon | Accounts Receivable | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage		20.00%
Tepatguna | Accounts Receivable | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage		18.00%

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=51801978&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=51801978&loc=d3e6404-108592

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-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
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-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13537-108611

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