Summary of Significant Accounting Policies (Narrative) (Details) - ft² ft² in Millions	1 Months Ended	3 Months Ended
	Feb. 28, 2017	Mar. 31, 2017
Significant Accounting Policies [Line Items]
Deferred compensation plan, period to diversify common shares after vesting	6 months
Square footage of operating properties (in square feet)		44.4
Base Minimum Rental Revenue [Member] | Tenant Base [Member]
Significant Accounting Policies [Line Items]
Concentrations of risk (percentage)		3.00%
Base Minimum Rental Revenue [Member] | Houston, Texas Geographic Concentration [Member]
Significant Accounting Policies [Line Items]
Concentrations of risk (percentage)		20.30%
Base Minimum Rental Revenue [Member] | Other Parts of Texas Geographic Concentration [Member]
Significant Accounting Policies [Line Items]
Concentrations of risk (percentage)		8.90%