Property Dispositions and Assets Held for Sale (Details) (USD $)	3 Months Ended								12 Months Ended			1 Months Ended
	Dec. 31, 2012 sqft	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 sqft	Dec. 31, 2011	Dec. 31, 2010	May 31, 2011 Property at 28 West 44th Street sqft	Feb. 29, 2012 292 Madison Avenue	Sep. 30, 2010 Property at 19 West 44th Street sqft	Oct. 31, 2012 44th West 55th Street Pro Forma
Property Dispositions and Assets Held for Sale
Consideration for sale of property												$ 161,000,000	$ 85,000,000	$ 123,200,000	$ 6,300,000
Square footage of property	29,685,079								29,685,079			359,000		292,000
Gain on sale of property				6,627,000			46,085,000		6,627,000	46,085,000	35,485,000	46,100,000	6,600,000	35,500,000
Employee compensation award													1,500,000	500,000
Revenues
Rental revenue									3,357,000	12,636,000	22,912,000
Escalation and reimbursement revenues									31,000	873,000	4,683,000
Other income									8,189,000	60,000	881,000
Total revenues									11,577,000	13,569,000	28,476,000
Operating expense									714,000	1,654,000	7,403,000
Real estate taxes									95,000	1,033,000	4,776,000
Transaction related costs									160,000
Interest expense, net of interest income									1,410,000	4,253,000	2,998,000
Amortization of deferred financing costs										172,000	883,000
Depreciation and amortization									82,000	676,000	5,326,000
Marketing, general and administrative and transaction related costs										1,000	26,000
Total expenses									2,461,000	7,789,000	21,412,000
Net income from discontinued operations	$ 9,126,000	$ 217,000	$ (67,000)	$ (160,000)	$ 1,116,000	$ 1,116,000	$ 1,675,000	$ 1,873,000	$ 9,116,000	$ 5,780,000	$ 7,064,000