Securitizations and Variable Interest Entities - Summary of Personal Whole Loan Securitizations and Sales (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Unconsolidated Trusts
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Principal derecognized from loans securitized or sold	$ 0	$ 0	$ 0	$ 255,203,000
Net gains recognized from loans securitized or sold	0	0	0	(20,000)
Fair value of asset-backed senior and subordinated securities, and CLUB Certificate asset-backed securities retained upon settlement			0	12,707,000
Cash proceeds from loans securitized or sold			0	237,764,000
Cash proceeds from servicing and other administrative fees on loans securitized or sold	2,021,000	4,176,000	7,546,000	14,118,000
Cash proceeds for interest received on senior securities and subordinated securities	377,000	983,000	2,198,000	3,792,000
Unconsolidated Certificate Program Trusts
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Principal derecognized from loans securitized or sold	0	233,852,000	0	871,489,000
Net gains recognized from loans securitized or sold	0	1,563,000	0	7,159,000
Fair value of asset-backed senior and subordinated securities, and CLUB Certificate asset-backed securities retained upon settlement			0	31,423,000
Cash proceeds from loans securitized or sold			0	598,515,000
Cash proceeds from servicing and other administrative fees on loans securitized or sold	3,131,000	6,697,000	12,054,000	20,919,000
Cash proceeds for interest received on senior securities and subordinated securities	$ 598,000	$ 1,847,000	4,388,000	6,740,000
Structured Program Transactions
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Transferor's interests retained in transferred financial assets, fair value			$ 0
Structured Program Transactions | Senior securities
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Transferor's interests retained in transferred financial assets, fair value				23,000,000
Structured Program Transactions | CLUB Certificate asset-backed securities
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Transferor's interests retained in transferred financial assets, fair value				18,300,000
Structured Program Transactions | Subordinated securities
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Transferor's interests retained in transferred financial assets, fair value				$ 2,900,000