Property Dispositions (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended			1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Aug. 30, 2013 West 34th Street 333 [Member]	Sep. 30, 2013 300 Main Street	Jun. 30, 2013 300 Main Street	Feb. 28, 2013 West 44 Street 55 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration for sale of property					$ 220,300,000	$ 13,500,000		$ 6,300,000
Impairment charge for assets held for sale						2,200,000	2,200,000
Gain on sale of property	13,787,000	0	14,900,000	6,627,000	13,800,000			1,100,000
Net proceeds from the sale					211,000,000
Revenues
Rental revenue	1,696,000	5,446,000	10,656,000	13,872,000
Escalation and reimbursement revenues	683,000	611,000	1,292,000	1,778,000
Other income	1,000	(376,000)	8,000	(376,000)
Total revenues	2,380,000	5,681,000	11,956,000	15,274,000
Operating expense	660,000	2,065,000	3,643,000	4,930,000
Real estate taxes	187,000	302,000	765,000	916,000
Interest expense, net of interest income	130,000	696,000	461,000	1,627,000
Depreciable real estate reserves	0	0	2,150,000	0
Transaction related costs	(3,000)	65,000	0	160,000
Depreciation and amortization	0	1,602,000	3,212,000	4,758,000
Total expenses	974,000	4,730,000	10,231,000	12,391,000
Net income (loss) from discontinued operations	$ 1,406,000	$ 951,000	$ 1,725,000	$ 2,883,000