Commitments and Contingencies (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011 squarefeet properties percentage	Sep. 30, 2010	Sep. 30, 2011 squarefeet properties percentage	Sep. 30, 2010	Dec. 31, 2010
Commitments And Contingencies [Line Items]
Operating ground lease expense	$ 6,000	$ 170,000	$ 240,000	$ 558,000
Additional capital contributions to unconsolidated joint ventures	1,400,000		1,400,000
Letter of credit obligations	934,000		934,000
Development in Process	41,907,000		41,907,000		0
Number of Development Buildings Under Commitment	7		7
Leasable space of buildings	1,500,000		1,500,000
Anticipated aggregate investment	171,500,000		171,500,000
Potential payments for tenant allowances	43,600,000		43,600,000
Maximum [Member]
Commitments And Contingencies [Line Items]
Other miscellaneous guarantees related to unconsolidated joint ventures	$ 567,000		$ 567,000