Significant Tenants (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Oct. 31, 2014
Real Estate Properties [Line Items]
Real estate revenue, net (in dollars)	$ 52,036	$ 49,468
Bloomberg [Member]
Real Estate Properties [Line Items]
Leases Expiration Date			December 2015
Bloomberg [Member] | 731 Lexington Avenue [Member]
Real Estate Properties [Line Items]
Square Footage of Real Estate Property (in square feet)			188,608
Lease renewal term			5 years
Bloomberg [Member] | Customer Concentration Risk [Member]
Real Estate Properties [Line Items]
Real estate revenue, net (in dollars)		22,017
Percentage Of Minimum Revenue Threshold Contributed By One Tenant (in percentage)	10.00%
Bloomberg [Member] | Customer Concentration Risk [Member] | Sales Revenue Services Net [Member]
Real Estate Properties [Line Items]
Real estate revenue, net (in dollars)	$ 23,402
Percentage Rent Contributed By Tenant	45.00%	45.00%