Investment in 111 West 57th Partners LLC (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013 sqft	Jun. 30, 2013 sqft
Investment in 111 West 57th Partners LLC [Abstract]
Amount of the investment	$ 56,000,000	$ 56,000,000
Percentage ownership (in hundredths)	59.00%	59.00%
Additional indirect contribution	1,250,000	1,250,000
Additional ownership acquired through indirect contribution (in hundredths)	1.30%	1.30%
Additional contributions made by other partners in the agreement	37,750,000	37,750,000
Description of partnership agreement distribution		The JV Agreement and related operating agreements generally provide that all distributable cash shall be distributed as follows: (i) first, 100% to the members in proportion to their percentage interests until Investment LLC has received distributions yielding a 20% internal rate of return as calculated; (ii) second, 100% to the Sponsor as a return of (but not a return on) any additional capital contributions made by the Sponsor on account of manager overruns; and (iii) thereafter, (a) 50% to the members in proportion to their respective percentage interests at the time of such distribution, and (b) fifty percent 50% to the Sponsor.
Number of purchase agreements	3	3
Cost for inclusionary zoning rights	6,500,000	6,500,000
Area of Real Estate Property	346,000	346,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	867,000	867,000
Equity Method Investment, Summarized Financial Information, Assets [Abstract]
Real estate held for development, net	243,405,000	243,405,000
Escrow deposits	57,995,000	57,995,000
Other assets	22,497,000	22,497,000
Equity Method Investment, Summarized Financial Information, Assets, Total	323,897,000	323,897,000
Equity Method Investment, Summarized Financial Information, Liabilities [Abstract]
Mortgage payable	230,000,000	230,000,000
Accounts payable	354,000	354,000
Total liabilities	230,354,000	230,354,000
Equity:
Total equity	93,543,000	93,543,000
Total liabilities and equity	323,897,000	323,897,000
Income (Loss) [Abstract]
Rental income	15,000	15,000
Equity Method Investment, Summarized Financial Information, Cost of Sales	35,000	35,000
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss)	$ (20,000)	$ (20,000)