Property Dispositions and Assets Held for Sale (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended		9 Months Ended
	Sep. 30, 2012 sqft	Sep. 30, 2011	Sep. 30, 2012 sqft	Sep. 30, 2011	May 31, 2011 Property at 28 West 44th Street sqft	Feb. 29, 2012 292 Madison Avenue	Sep. 30, 2012 292 Madison Avenue
Property Dispositions and Assets Held for Sale
Consideration for sale of property					$ 161,000,000	$ 85,000,000
Square footage of property	29,537,460		29,537,460		359,000
Gain on sale of property			6,627,000	46,085,000	46,100,000		6,600,000
Revenues
Rental revenue	1,626,000	1,950,000	2,142,000	10,685,000
Escalation and reimbursement revenues				873,000
Other income (loss)	(376,000)		(376,000)	60,000
Total revenues	1,250,000	1,950,000	1,766,000	11,618,000
Operating expense	435,000	3,000	431,000	1,648,000
Real estate taxes				1,034,000
Transaction related costs	65,000		65,000
Interest expense, net of interest income	527,000	825,000	1,125,000	3,429,000
Amortization of deferred financing costs		6,000		166,000
Depreciation and amortization				676,000
Total expenses	1,027,000	834,000	1,621,000	6,953,000
Net income from discontinued operations	$ 223,000	$ 1,116,000	$ 145,000	$ 4,665,000