Preferred and Common Units of the Operating Partnership (Details Textuals) - USD ($)	1 Months Ended		3 Months Ended
	Jul. 31, 2015	Oct. 31, 2014	Mar. 31, 2016	Dec. 31, 2016	Jul. 01, 2015	Dec. 31, 2014	Oct. 01, 2014
Class of Stock [Line Items]
Common stock, shares issued					3,733,766
Shares issued, price per share					$ 66.19
At market stock aggregate gross sales price of common stock					$ 249,800,000	$ 300,000,000
Aggregate net proceeds after sales agent compensation	$ 249,600,000
Brannan St Project [Member]
Class of Stock [Line Items]
Business acquisition, equity interest issued or issuable, number of shares			867,701
Share price			$ 55.36
Common stock, par value			$ 0.01	$ 0.01
SFFGA [Member]
Class of Stock [Line Items]
Common stock, shares issued							351,476
Purchase price, value of shares issued to acquire land		$ 21,600,000