Loans - Secured Loans Designated as Impaired Loans (Details) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2021 USD ($) Loan	Dec. 31, 2020 USD ($) Loan
Secured Loans Designated as Impaired Loans [Abstract]
Number of loans | Loan		4	3
Principal		$ 6,370	$ 15,139
Recorded investment	[1]	6,532	15,531
Impaired loans without allowance		$ 6,532	$ 15,531
Weighted average LTV, at origination		51.40%	54.00%

[1] Recorded investment is the sum of principal, advances, and accrued interest for financial reporting purposes.