Leasing Activity (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) lease	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Number of leases | lease	1
Concentration risk, percentage	100.00%	100.00%	100.00%
Office Building | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%
Revenue | Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%
Missouri | Revenue | Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	65.00%
Texas | Revenue | Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	26.00%
Colorado | Revenue | Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	9.00%
Chase Park Plaza | Revenue | Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	66.00%
Frisco Square | Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	19.00%
Frisco Square | Revenue | Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	19.00%
Hotel | Revenue | Asset type Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	75.00%
Office Building | Revenue | Asset type Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	17.00%
Multifamily | Revenue | Asset type Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	8.00%
Northpoint Central
Concentration Risk [Line Items]
Rental revenue | $	$ 1
Northpoint Central | Rental revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%
Northpoint Central | Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	2.00%