Concentrations (Narrative) (Details)	3 Months Ended
	Mar. 31, 2013 property	Mar. 31, 2012
Uptown Park In Houston, Texas [Member]
Concentration Risk [Line Items]
Percentage of individual property to total assets	17.00%
Houston Properties [Member]
Concentration Risk [Line Items]
Number of operating properties	20
Percentage of individual income on base rental income	52.00%	62.20%
Preston Royal West In Dallas, Texas [Member]
Concentration Risk [Line Items]
Percentage of individual property to total assets	10.80%