Related Party Transactions (Details) (USD $)			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Alliance Building Services	Sep. 30, 2012 Alliance Building Services	Sep. 30, 2013 Alliance Building Services	Sep. 30, 2012 Alliance Building Services	Sep. 30, 2013 A-List Marketing, LLC	Sep. 30, 2012 A-List Marketing, LLC	Sep. 30, 2013 A-List Marketing, LLC	Sep. 30, 2012 A-List Marketing, LLC	Sep. 30, 2013 Nancy Peck and Company sqft	Sep. 30, 2013 Entity with Stephen L Green ownership interest	Sep. 30, 2012 Entity with Stephen L Green ownership interest	Sep. 30, 2013 Entity with Stephen L Green ownership interest	Sep. 30, 2012 Entity with Stephen L Green ownership interest
Related Party Transactions
Profit participation from related party			$ 800,000	$ 800,000	$ 2,700,000	$ 2,400,000
Payments made for services			4,800,000	4,700,000	13,200,000	12,900,000	50,700	2,400	158,000	58,300
Space at 420 Lexington Avenue leased (in square feet)											1,003
Lease rent due per year											35,516
Increased lease rent due per year beginning in year seven											40,000
Property management fees from related party												105,000	93,000	319,000	292,000
Due from joint ventures	2,128,000	511,000
Other	5,672,000	7,020,000
Related party receivables	7,800,000	7,531,000
Due to joint venture (included in Accounts payable and accrued expenses)	$ 0	$ (8,401,000)