Real Estate Activity During the Six Months Ended June 30, 2014 (Narrative) (Details) (USD $) In Millions, unless otherwise specified				0 Months Ended
	Jun. 11, 2014 Patriots park [Member] sqft Buildings	May 20, 2014 10 CityPoint [Member] sqft	May 20, 2014 888 Boylston Street [Member] sqft	Apr. 10, 2014 Salesforece Tower (formerly Transbay Tower) [Member] sqft floor	Apr. 03, 2014 Six Nine Zero Folsom Street [Member] sqft	Apr. 01, 2014 Nine Nine Third Avenue [Member] sqft	Feb. 10, 2014 The Avant at Reston Town Center Residential [Member] apartments sqft	Apr. 10, 2014 Company [Member] Salesforece Tower (formerly Transbay Tower) [Member]
Real Estate Properties [Line Items]
Contractual Sales Price	$ 321.0
Number of real estate properties	3
Number of apartment units							359
Net Rentable Area (in sf)	706,000	245,000	425,000	1,400,000	26,000	17,000	355,000
Ownership Percentage								95.00%
Square Footage Of Signed Lease				714,000
Number of floors real estate				61