Discontinued Operations and Gain on Disposition of Rental Properties (Details 3) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	$ 1,276,000	$ 0	$ 28,100,000	$ 21,471,000
Promenade Bolingbrook [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	1,276,000	0	1,276,000	0
Quartermaster Plaza [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	0	0	26,373,000	0
Mesa del Sol - 5600 University SE [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	0	0	451,000	0
Millender Center [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	0	0	0	21,660,000
Other [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	$ 0	$ 0	$ 0	$ (189,000)