Related Party Transactions (Details) (USD $)			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Alliance Building Services	Jun. 30, 2012 Alliance Building Services	Jun. 30, 2013 Alliance Building Services	Jun. 30, 2012 Alliance Building Services	Jun. 30, 2013 A-List Marketing, LLC	Jun. 30, 2012 A-List Marketing, LLC	Jun. 30, 2013 A-List Marketing, LLC	Jun. 30, 2012 A-List Marketing, LLC	Jun. 30, 2013 Nancy Peck and Company sqft	Jun. 30, 2013 Entity with Stephen L Green ownership interest	Jun. 30, 2012 Entity with Stephen L Green ownership interest	Jun. 30, 2013 Entity with Stephen L Green ownership interest	Jun. 30, 2012 Entity with Stephen L Green ownership interest
Related Party Transactions
Profit participation from related party			$ 900,000	$ 800,000	$ 1,900,000	$ 1,600,000
Payments made for services			4,200,000	4,700,000	8,400,000	8,200,000	105,000	44,200	107,000	55,900
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												96,000	110,000	214,000	199,000
Amounts due from/to related parties
Due from joint ventures	1,777,000	511,000
Other	5,068,000	7,020,000
Related party receivables	6,845,000	7,531,000
Due to joint venture (included in Accounts payable and accrued expenses)		$ (8,401,000)