Commitments and Contingencies (Details 3) (USD $)			12 Months Ended	1 Months Ended	12 Months Ended						1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 420 Lexington Avenue	Jul. 31, 2016 711 Third Avenue	Dec. 31, 2012 711 Third Avenue	Dec. 31, 2012 461 Fifth Avenue item	Dec. 31, 2012 625 Madison Avenue item	Dec. 31, 2012 1185 Avenue of the Americas	Dec. 31, 2012 673 First Avenue	Dec. 31, 2011 673 First Avenue	Oct. 31, 2012 1080 Amsterdam Avenue	Dec. 31, 2012 1080 Amsterdam Avenue
Commitments and Contingencies
Required annual ground lease payments			$ 10,900,000	$ 5,500,000	$ 5,250,000	$ 2,100,000	$ 4,600,000	$ 6,900,000
Required annual ground lease payments, prior to reset					1,550,000
Percentage of fee not owned by the entity					50.00%
Number of renewal options available						2	2
Term of first renewal option						21 years	23 years	23 years
Term of second renewal option						21 years	23 years
Term of third renewal option						15 years
Land as percentage of fair market value of the property									70.00%
Initial lease term									49 years
Term of renewal option									25 years
Capital lease, cost basis	40,340,000	12,208,000							12,200,000			28,100,000
Cumulative amortization									6,300,000	6,000,000
Prepayment of ground lease rent											$ 13,000,000
Value of land as a percentage of the fair market value of the property											40.00%
Extension in lease term									50 years