Discontinued Operations and Gain (Loss) on Disposition of Rental Properties (Details 1)	Dec. 31, 2014 apartmentunit
Millender Center [Member]
Summary of rental properties included in discontinued operations
Number of Units	339
Emerald Palms [Member]
Summary of rental properties included in discontinued operations
Number of Units	505
Southfield [Member]
Summary of rental properties included in discontinued operations
Number of Units	212
Promenade Bolingbrook [Member]
Summary of rental properties included in discontinued operations
Square Feet	771,000
Quartermaster Plaza [Member]
Summary of rental properties included in discontinued operations
Square Feet	456,000
Mesa del Sol - 5600 University SE [Member]
Summary of rental properties included in discontinued operations
Square Feet	87,000
Orchard Town Center [Member]
Summary of rental properties included in discontinued operations
Square Feet	603,000
Colorado Studios [Member]
Summary of rental properties included in discontinued operations
Square Feet	75,000
Higbee Building [Member]
Summary of rental properties included in discontinued operations
Square Feet	815,000
Sheraton Station Square [Member]
Summary of rental properties included in discontinued operations
Number of Units	399
Fairmont Plaza [Member]
Summary of rental properties included in discontinued operations
Square Feet	335,000
White Oak Village [Member]
Summary of rental properties included in discontinued operations
Square Feet	843,000
Quebec Square [Member]
Summary of rental properties included in discontinued operations
Square Feet	739,000
Seven triple net lease properties [Member]
Summary of rental properties included in discontinued operations
Square Feet	422,000