Subsequent Events (Details) $ in Thousands	Apr. 27, 2018 USD ($) ft²	Apr. 26, 2018	Apr. 23, 2018 USD ($) ft² a yr Buildings	Apr. 19, 2018 USD ($) ft² yr apartments	Apr. 24, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Subsequent Event [Line Items]
Mortgage notes payable, net						$ 2,974,930	$ 2,979,281
Unsecured term loan						$ 0	$ 0
Delayed Draw Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Unsecured term loan					$ 500,000
Interest Rate Based on LIBOR or CDOR [Member] | Delayed Draw Facility [Member]
Subsequent Event [Line Items]
Margin added to Calculated Interest Rate						0.90%
Interest Rate Based on LIBOR or CDOR [Member] | Delayed Draw Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Margin added to Calculated Interest Rate					0.90%
The Hub on Causeway - Residential [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage				50.00%
Construction Loan Facility Borrowing Capacity				$ 180,000
Debt Instrument, Basis Spread on Variable Rate				2.00%
Number of extensions				2
Extension Option (in years) | yr				1
Number of apartment units | apartments				440
Net Rentable Area (in sf) | ft²				320,000
540 Madison Avenue [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage	60.00%
Mortgage notes payable, net	$ 120,000
Debt Instrument, Basis Spread on Variable Rate	1.10%	1.50%
Net Rentable Area (in sf) | ft²	284,000
Santa Monica Business Park [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Net purchase price			$ 616,000
Area of Land | a			47
number of buildings | Buildings			21
Net Rentable Area (in sf) | ft²			1,200,000.0
rentable square feet subject to a ground lease (percetnage)			70.00%
Term of Lease Signed (in years) | yr			80