Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Discontinued Operations and Disposal Groups [Abstract]
Rental and other revenues																	$ 1,593		$ 3,627		$ 11,292
Operating expenses:
Rental property and other expenses																	570		1,406		4,263
Depreciation and amortization																	127		744		2,231
Impairment of assets held for use																	0		0		10,964
Total operating expenses																	697		2,150		17,458
Interest expense																	0		0		67
Other income																	1		2		3
Income/(loss) from discontinued operations																	897		1,479		(6,230)
Net gains/(losses) on disposition of discontinued operations																	2,573		(86)		21,466
Total discontinued operations	0	[1]	2,842	[1]	291	[1]	337	[1]	246	[1]	272	[1]	238	[1]	637	[1]	3,470		1,393		15,236
Carrying value of assets held for sale and assets sold that qualified for discontinued operations during the year	15,261								42,133								15,261		42,133		97,457
Assets:
Land	0								2,788								0		2,788
Buildings and tenant improvements	0								12,707								0		12,707
Land held for development	0								4,536								0		4,536
Less accumulated depreciation	0								(5,012)								0		(5,012)
Net real estate assets	0								15,019								0		15,019
Accrued straight line rents receivable	0								57								0		57
Deferred leasing costs, net	0								257								0		257
Prepaid expenses and other assets	0								43								0		43
Real estate and other assets, net, held for sale	0								15,376								0		15,376
Tenant security deposits, deferred rents and accrued costs	$ 0	[2]							$ 11	[2]							$ 0	[2]	$ 11	[2]

[1] The amounts presented may not equal to the amounts previously reported in the most recent Form 10-Qs or prior 10-K for each period as a result of discontinued operations.

[2] Included in accounts payable, accrued expenses and other liabilities.