Property Transactions (Gain (Loss) on Sales of Discontinued Operations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	$ 18,407	$ 8,519	$ 7,216
Third party management and leasing business [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	7,459	0	0
The Avenue Forsyth [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	4,508	0	(10)
The Avenue Webb Gin [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	3,590	0	0
Cosmopolitan Center [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	2,064	0	0
Galleria 75 [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	569	0	0
The Avenue Collierville [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	73	0	0
King Mill Distribution Park - Building 3 [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	307	4,977	0
One Georgia Center [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	(104)	2,805	0
Lakeside Ranch Business Park - Building 20 [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	(59)	1,121	0
Jefferson Mill Business Park - Building A [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	0	(394)	0
San Jose Market Center [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	0	10	6,572
8995 Westside Parkway [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	$ 0	$ 0	$ 654