Real Estate - Real Estate Under Development and Construction in Progress - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Notes receivable, net | $	$ 101,450	$ 114,943	$ 111,775	$ 160,991
Impairment charge | $	72,842
Fund II
Property, Plant and Equipment [Line Items]
Notes receivable, net | $	$ 33,800
Fund IV
Property, Plant and Equipment [Line Items]
Number of projects put into service during period | property	1
Cortlandt Crossing | Fund III
Property, Plant and Equipment [Line Items]
Number of projects put into service during period | property	1
Fund Portfolio | Fund IV
Property, Plant and Equipment [Line Items]
Number of projects put into service during period | property	2
Impairment charge | $	$ 16,500
Core Portfolio
Property, Plant and Equipment [Line Items]
Number of projects put into service during period | property		1