Related Party Transactions (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Amounts due from/to related parties
Due from joint ventures	$ 511,000	$ 477,000
Other	7,020,000	3,524,000
Related party receivables	7,531,000	4,001,000
Due to joint venture (included in Accounts payable and accrued expenses)	(8,401,000)
Alliance Building Services
Related Party Transactions
Profit participation from related party	4,000,000	2,700,000	2,200,000
Payments made for services	17,900,000	16,100,000	14,200,000
A-List Marketing, LLC
Related Party Transactions
Payments made for services	155,500	140,300	86,300
Nancy Peck and Company
Related Party Transactions
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
Entity with Stephen L Green ownership interest
Related Party Transactions
Property management fees from related party	$ 384,900	$ 420,300	$ 390,700