Real Estate - Schedule of Development in Process Activities (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Sep. 30, 2021
Property, Plant and Equipment [Line Items]
Notes receivable, net	$ 101,450	$ 101,450	$ 158,468
Fund II
Property, Plant and Equipment [Line Items]
Notes receivable, net	33,800	33,800
Fund Portfolio
Property, Plant and Equipment [Line Items]
Notes receivable, net	33,800	33,800
Fund Portfolio | Fund IV
Property, Plant and Equipment [Line Items]
Impairment charge	$ 16,500	$ 16,500