Concentration of Credit Risk - Summary of Geographic Composition of Loans Held for Investment Based on Current UPB and Loan Commitment (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Retail
Loans And Leases Receivable Disclosure [Line Items]
Non-drawable outstanding unfunded loan commitments	$ 2.1	$ 2.1

Amount of undisbursed portion of financing receivable balance. Excludes financing receivable covered under loss sharing agreement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5066-111524

Name:	us-gaap_FinancingReceivableLoanInProcess
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant