Net Loss on Disposition of Partial Interest in Development Project (Details Textuals)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2014 a
Disposal Group, not including discontinued operations [Line Items]
Net loss on disposition of partial interest in development project	$ 0	$ 0	$ 0	$ 19,590,000
Greenland Joint Venture [Member]
Disposal Group, not including discontinued operations [Line Items]
Percentage of ownership sold						70.00%
Cash purchase price received, net of transaction costs					$ 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]
Disposal Group, not including discontinued operations [Line Items]
Area of project (in acres) | a						22