Concentration of Risk - Concentrations of Loans Unpaid Principal Balance (Details) - Commercial Property - Originates and Purchases Loans Secured	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
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	55.00%	52.70%
Property Type Concentration | Mixed use
Concentration Risk [Line Items]
Concentration risk, percentage	11.70%	12.60%
Property Type Concentration | Retail
Concentration Risk [Line Items]
Concentration risk, percentage	8.40%	8.70%
Property Type Concentration | Multifamily
Concentration Risk [Line Items]
Concentration risk, percentage	7.80%	8.60%
Property Type Concentration | Warehouse
Concentration Risk [Line Items]
Concentration risk, percentage	6.50%	5.70%
Property Type Concentration | Office
Concentration Risk [Line Items]
Concentration risk, percentage	5.40%	6.40%
Property Type Concentration | Other (individually less than 5.0%)
Concentration Risk [Line Items]
Concentration risk, percentage	5.20%	5.30%
California | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	22.00%	22.80%
New York | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	18.30%	19.90%
Florida | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	13.40%	13.30%
New Jersey | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	7.30%	7.50%
Other states (individually less than 5.0%) | Geographic Concentration
Concentration Risk [Line Items]
Concentration risk, percentage	39.00%	36.50%