Discontinued Operations and Gain on Disposition of Rental Properties (Details)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended
	Jun. 30, 2014 Millender Center [Member]	Jun. 30, 2013 Millender Center [Member]	Jun. 30, 2014 Millender Center [Member] apartmentunit	Jun. 30, 2013 Millender Center [Member]	Jun. 30, 2014 Promenade Bolingbrook [Member]	Jun. 30, 2013 Promenade Bolingbrook [Member]	Jun. 30, 2014 Promenade Bolingbrook [Member] sqft	Jun. 30, 2013 Promenade Bolingbrook [Member]	Jun. 30, 2014 Quartermaster Plaza [Member]	Jun. 30, 2013 Quartermaster Plaza [Member]	Jun. 30, 2014 Quartermaster Plaza [Member] sqft	Jun. 30, 2013 Quartermaster Plaza [Member]	Jun. 30, 2014 Mesa del Sol - 5600 University SE [Member]	Jun. 30, 2013 Mesa del Sol - 5600 University SE [Member]	Jun. 30, 2014 Mesa del Sol - 5600 University SE [Member] sqft	Jun. 30, 2013 Mesa del Sol - 5600 University SE [Member]	Jun. 30, 2014 Orchard Town Center [Member]	Jun. 30, 2013 Orchard Town Center [Member]	Jun. 30, 2014 Orchard Town Center [Member] sqft	Jun. 30, 2013 Orchard Town Center [Member]	Jun. 30, 2014 Colorado Studios [Member]	Jun. 30, 2013 Colorado Studios [Member]	Jun. 30, 2014 Colorado Studios [Member] sqft	Jun. 30, 2013 Colorado Studios [Member]	Jun. 30, 2014 Higbee Building [Member]	Jun. 30, 2013 Higbee Building [Member]	Jun. 30, 2014 Higbee Building [Member] sqft	Jun. 30, 2013 Higbee Building [Member]	Jun. 30, 2014 Sheraton Station Square [Member]	Jun. 30, 2013 Sheraton Station Square [Member]	Jun. 30, 2014 Sheraton Station Square [Member] room	Jun. 30, 2013 Sheraton Station Square [Member]	Jun. 30, 2014 Two triple net lease properties [Member]	Jun. 30, 2013 Two triple net lease properties [Member]	Jun. 30, 2014 Two triple net lease properties [Member] sqft		Jun. 30, 2013 Two triple net lease properties [Member]	Dec. 31, 2013 One triple net lease property [Member] property	Mar. 31, 2013 One triple net lease property [Member] property
Summary of rental properties included in discontinued operations
Location			Detroit, Michigan				Bolingbrook, Illinois				Philadelphia, Pennsylvania				Albuquerque, New Mexico				Westminster, Colorado				Denver, Colorado				Cleveland, Ohio				Pittsburgh, Pennsylvania				Various
Square feet							771,000				456,000				87,000				603,000				75,000				815,000								138,000
Number of units/rooms			339																												399
Period disposed			Q1-2013				Q2-2014				Q1-2014				Q1-2014				Q4-2013				Q3-2013				Q3-2013				Q3-2013				Various	[1]
Period status	0	0	0	Yes	Yes	Yes	Yes	Yes	0	Yes	Yes	Yes	0	Yes	Yes	Yes	0	Yes	0	Yes	0	Yes	0	Yes	0	Yes	0	Yes	0	Yes	0	Yes	0	Yes	0		Yes
Number of triple net lease properties disposed of																																						1	1

[1] Includes one triple net lease property disposed of during Q4-2013 and one triple net lease property disposed of during Q1-2013.