Property Dispositions and Assets Held for Sale (Details) (USD $)	3 Months Ended		6 Months Ended		1 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Feb. 29, 2012 292 Madison Avenue	Feb. 28, 2013 44th West 55th Street	Jun. 30, 2013 333 West 34th Street	Mar. 31, 2013 300 Main Street	Jun. 30, 2013 300 Main Street
Property Dispositions and Assets Held for Sale
Consideration for sale of property					$ 85,000,000	$ 6,300,000	$ 220,300,000	$ 13,500,000
Impairment charge for assets held for sale									2,200,000
Gain on sale of property			1,113,000	6,627,000	6,600,000	1,100,000
Revenues
Rental revenue	4,930,000	3,853,000	8,960,000	8,425,000
Escalation and reimbursement revenues	155,000	618,000	609,000	1,167,000
Other income			7,000
Total revenues	5,085,000	4,471,000	9,576,000	9,592,000
Operating expense	1,542,000	1,488,000	2,983,000	2,866,000
Real estate taxes	284,000	313,000	578,000	614,000
Interest expense, net of interest income	167,000	166,000	331,000	930,000
Depreciable real estate reserves	2,150,000		2,150,000
Transaction related costs	3,000		3,000	95,000
Depreciation and amortization	1,617,000	1,605,000	3,211,000	3,156,000
Total expenses	5,763,000	3,572,000	9,256,000	7,661,000
Net income (loss) from discontinued operations	$ (678,000)	$ 899,000	$ 320,000	$ 1,931,000