Related Party Transactions - Schedule of Balance Sheet of Related Party Transaction (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Beneficial interests in securitization trusts
Related Party Transaction [Line Items]
Carrying value	$ 139,494	$ 91,418
Receivable from servicer | Gregory
Related Party Transaction [Line Items]
Amount of transaction	18,128	15,755
Mortgage loans held-for-investment, net | Gregory
Related Party Transaction [Line Items]
Amount of transaction		1,838
Mortgage loans held-for-investment, net | Gaea Real Estate Corp.
Related Party Transaction [Line Items]
Amount of transaction	10,025	11,000
Management fee payable | Thetis Asset Management LLC
Related Party Transaction [Line Items]
Amount of transaction	2,289	2,247
Prepaid expenses and other assets
Related Party Transaction [Line Items]
Amount of transaction	1,354	876
Prepaid expenses and other assets | Thetis Asset Management LLC
Related Party Transaction [Line Items]
Amount of transaction		18
Accrued expenses and other liabilities | Gregory
Related Party Transaction [Line Items]
Amount of transaction	$ (92)	$ (44)