Real Estate - Schedule of Acquisitions and Conversions (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Purchase Price	$ 260,344	$ 186,463
Core Portfolio
Business Acquisition [Line Items]
Purchase Price	$ 82,440	$ 1,337
Core Portfolio | 849 and 912 W. Armitage - Chicago, IL
Business Acquisition [Line Items]
Percent Acquired	100.00%
Purchase Price	$ 7,802
Core Portfolio | Soho Acquisitions | 41, 47, 51 and 53 Greene Street - New York, NY
Business Acquisition [Line Items]
Percent Acquired	100.00%
Purchase Price	$ 74,638
Core Portfolio | Bedford Green Land Parcel | Bedford Hills N Y
Business Acquisition [Line Items]
Percent Acquired		100.00%
Purchase Price		$ 1,337
Fund V
Business Acquisition [Line Items]
Purchase Price	$ 177,904	$ 149,022
Fund V | Palm Coast Landing | Palm Coast, FL
Business Acquisition [Line Items]
Percent Acquired	100.00%
Purchase Price	$ 36,644
Fund V | Trussville Promenade - Trussville, AL | Trussville, AL
Business Acquisition [Line Items]
Percent Acquired		100.00%
Purchase Price		$ 45,259
Fund V | Lincoln Commons | Lincoln, RI
Business Acquisition [Line Items]
Percent Acquired	100.00%
Purchase Price	$ 54,299
Fund V | Elk Grove Commons - Elk Grove, CA | Elk Grove, CA
Business Acquisition [Line Items]
Percent Acquired		100.00%
Purchase Price		$ 59,320
Fund V | Landstown Commons | Virginia Beach, VA
Business Acquisition [Line Items]
Percent Acquired	100.00%
Purchase Price	$ 86,961
Fund V | Hiram Pavilion | Hiram G A
Business Acquisition [Line Items]
Percent Acquired		100.00%
Purchase Price		$ 44,443
Fund IV
Business Acquisition [Line Items]
Purchase Price		$ 36,104
Fund IV | Broughton Street Partners I | Savannah G A
Business Acquisition [Line Items]
Percent Acquired		100.00%
Purchase Price		$ 36,104