Investments in Unconsolidated Joint Ventures (Details) (USD $)	3 Months Ended	9 Months Ended		6 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended
	Jun. 30, 2010 Building	Sep. 30, 2011	Sep. 30, 2010	Jun. 30, 2010 Forest City Enterprises [Member] Building	Sep. 30, 2011 Forest City Enterprises [Member]	Feb. 22, 2010 Forest City Enterprises [Member] Building	Dec. 31, 2010 National Medical Office Building [Member]	Sep. 30, 2011 National Medical Office Building [Member] Property
Schedule of Equity Method Investments [Line Items]
Interest in seven-building life science campus					49.00%
Number of buildings acquired	7
Number of building closed				1		6
Percentage of leased portion of the seven-building life science campus portfolio				100.00%
Equity method investments		$ 779,000	$ 174,692,000	$ 174,692,000			$ 21,321,000	$ 729,000
Approximate share of the non-recourse secured debt assumed by the joint venture				156,729,000			24,609,000	3,668,000
Weighted-average interest rates of non-recourse secured debt assumed by the joint venture				7.10%			6.06%	4.50%
Unamortized investment in joint venture primarily attributable to real estate and related intangible assets					$ 8,814,000			$ 70,000
Number of medical office buildings under construction								2