Concentration of Risk - Concentrations of Loans Unpaid Principal Balance (Details) - Commercial Property - Originates and Purchases Loans Secured	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	100.00%	100.00%
Property Type Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	100.00%	100.00%
Property Type Concentration | Investor 1-4
Concentration Risk [Line Items]
Concentration risk, percentage	52.70%	50.70%
Property Type Concentration | Mixed use
Concentration Risk [Line Items]
Concentration risk, percentage	12.60%	12.80%
Property Type Concentration | Retail
Concentration Risk [Line Items]
Concentration risk, percentage	8.70%	9.10%
Property Type Concentration | Multifamily
Concentration Risk [Line Items]
Concentration risk, percentage	8.60%	8.80%
Property Type Concentration | Office
Concentration Risk [Line Items]
Concentration risk, percentage	5.70%	6.10%
Property Type Concentration | Warehouse
Concentration Risk [Line Items]
Concentration risk, percentage	6.40%	6.70%
Property Type Concentration | Other (individually less than 5.0%)
Concentration Risk [Line Items]
Concentration risk, percentage	5.30%	5.80%
California | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	22.80%	23.30%
New York | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	19.90%	21.40%
Florida | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	13.30%	13.50%
New Jersey | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	7.50%	7.70%
Other states (individually less than 5.0%) | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	36.50%	34.10%