Investments in Unconsolidated Entities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		4 Months Ended	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	May 01, 2012 properties	Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Interest in seven-building life science campus				49.00%
Number of buildings acquired			3
Number of building closed			39
Equity method investments	$ 0	$ 602
Investment Percentage Range	10% to 50%
Forest City Enterprises [Member]
Schedule of Equity Method Investments [Line Items]
Number of buildings acquired				7
Equity method investments				174,962
Unamortized investment in joint venture primarily attributable to real estate and related intangible assets	$ 4,818