Investments in Unconsolidated Joint Ventures (Details) (USD $)	6 Months Ended				1 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2010 Forest City Enterprises [Member]	Feb. 22, 2010 Forest City Enterprises [Member]	Dec. 31, 2010 National Medical Office Building [Member]	Jun. 30, 2011 National Medical Office Building [Member]
Schedule of Equity Method Investments [Line Items]
Interest in seven-building life science campus			49.00%
Number of building closed			7	6
Percentage of leased portion of the seven-building life science campus portfolio			100.00%
Equity method investments	$ 779,000	$ 174,574,000	$ 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			$ 11,304,000			$ 231,000
Number of medical office buildings under construction						2