Preferred Equity Investments and Investments in Unconsolidated Real Estate Joint Ventures - Provision for credit losses (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2020
Provision for credit losses, beginning of the period	$ 16,153
Provision for credit loss	92		$ 223
Provision for credit losses, end of period	315	$ 16,153	16,153
Alexan Southside Place
Provision for credit loss	$ (15,930)	$ 15,900	$ 15,930