Net Loss on Disposition of Partial Interest in Development Project (Details Textuals)	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($) a	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($) a
Significant Acquisitions and Disposals [Line Items]
Net loss on disposition of partial interest in development project	$ 0	$ 19,590,000	$ 0	$ 19,590,000
Greenland Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Percentage of ownership sold		70.00%		70.00%
Cash purchase price received, net of transaction costs	$ 208,275,000		208,275,000
Net loss on disposition of partial interest in development project			19,590,000
Net loss on disposition of partial interest in development project, net of noncontrolling interests			$ 16,211,000
Pacific Park Brooklyn [Member]
Significant Acquisitions and Disposals [Line Items]
Area of project (in acres) | a		22		22