Discontinued Operations and Gain on Disposition of Rental Properties (Details 2) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	$ 0	$ 22,460,000	$ 28,100,000	$ 43,931,000
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
Promenade Bolingbrook [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	0	0	1,276,000	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
Higbee Building [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	0	2,922,000	0	2,922,000
Colorado Studios [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	0	1,239,000	0	1,239,000
Sheraton Station Square [Member]
Gain (Loss) on Disposition of Rental Properties [Line Items]
Pre-tax gain on disposition of rental properties	0	18,096,000	0	18,096,000
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	$ 203,000	$ 0	$ 14,000