Real Estate - Schedule of Acquisitions and Conversions (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Purchase Price	$ 32,194	$ 186,463
Core Portfolio
Business Acquisition [Line Items]
Purchase Price		$ 1,337
Core Portfolio | Soho Portfolio | 51 and 53 Greene Street
Business Acquisition [Line Items]
Percent Acquired	100.00%
Purchase Price	$ 32,194
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		$ 149,022
Fund V | Trussville Promenade - Trussville, AL | Trussville, AL
Business Acquisition [Line Items]
Percent Acquired		100.00%
Purchase Price		$ 45,259
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 | 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