Related Party Transactions (Details) (USD $)			3 Months Ended		6 Months Ended		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 Alliance Building Services Service Corporation	Jun. 30, 2012 Alliance Building Services Service Corporation	Jun. 30, 2013 Alliance Building Services Service Corporation	Jun. 30, 2012 Alliance Building Services Service Corporation	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 in which Stephen L Green owns interest	Jun. 30, 2012 Entity in which Stephen L Green owns interest	Jun. 30, 2013 Entity in which Stephen L Green owns interest	Jun. 30, 2012 Entity in which Stephen L Green owns 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 foot)															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 to/ from 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 a joint venture (included in Accounts payable and accrued expenses)		$ (8,401,000)