Summary of Significant Accounting Policies (Narrative) (Details) ft² in Millions	9 Months Ended
Sep. 30, 2016 ft²
Significant Accounting Policies [Line Items]
Square footage of operating properties (in square feet)	45.2
Base Minimum Rental Revenue [Member] \| Tenant Base [Member]
Significant Accounting Policies [Line Items]
Concentrations of risk (percentage)	3.10%
Base Minimum Rental Revenue [Member] \| Houston, Texas Geographic Concentration [Member]
Significant Accounting Policies [Line Items]
Concentrations of risk (percentage)	21.00%
Base Minimum Rental Revenue [Member] \| Other Parts of Texas Geographic Concentration [Member]
Significant Accounting Policies [Line Items]
Concentrations of risk (percentage)	9.70%

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://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=64851502&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=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

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