Real Estate Investments (Schedule of Annualized Rental Income by Major Tenant) (Details)	3 Months Ended
	Mar. 31, 2014 Worldwide Plaza Cravath, Swaine & Moore, LLP [Member]	Mar. 31, 2014 Worldwide Plaza Nomura Holdings America, Inc. [Member]	Mar. 31, 2013 229 West 36th Street American Language Communication Center, Inc. [Member]
Revenue, Major Customer [Line Items]
Major tenant rental income, as a percentage of total annualized rental income	18.20%	12.40%	10.50%