Multi-family Loans, at Fair Value - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net unrealized gains (losses)	$ 1.0	$ (1.5)
Loan premiums and early redemption	$ 2.5	$ 1.1	$ 3.8