Commitments and Contingencies (Details 2) (USD $)			12 Months Ended	1 Months Ended		12 Months Ended				1 Months Ended				1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 420 Lexington Avenue	Jul. 31, 2016 711 Third Avenue	Jul. 31, 2011 711 Third Avenue	Dec. 31, 2012 711 Third Avenue	Dec. 31, 2012 461 Fifth Avenue option	Dec. 31, 2012 625 Madison Avenue option	Dec. 31, 2012 1185 Avenue of the Americas	Nov. 30, 2012 673 First Avenue	Apr. 30, 1988 673 First Avenue	Dec. 31, 2012 673 First Avenue	Dec. 31, 2011 673 First Avenue	Oct. 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
Prepayment of ground lease rent														13,000,000
Value of land as a percentage of the fair market value of the property														40.00%
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		25 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
Extension in lease term										50 years
Capital lease, cost basis	40,340,000	12,208,000										12,200,000
Cumulative amortization												$ 6,300,000	$ 6,000,000	$ 28,100,000