Securitizations and Variable Interest Entities - Summary of Personal Whole Loan Securitizations and Sales (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Personal Whole Loan Securitization
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	$ 299,348	$ 350,854	$ 1,300,838	$ 687,512
Net gains (losses) recognized from loans securitized or sold	530	772	6,039	2,511
Fair value of senior securities and subordinated certificates received	14,869	18,529	65,653	36,065
Cash proceeds from loans securitized or sold	277,509	308,614	867,875	569,443
Cash proceeds from servicing and other administrative fees on loans securitized or sold	4,040	870	9,533	940
Cash proceeds for interest received on senior securities and subordinated certificates	742	102	2,044	102
Personal Whole Loan Securitization \| 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	13,500	16,100	57,300	30,100
Personal Whole Loan Securitization \| Subordinated residual certificates
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	1,400	$ 2,400	8,400	$ 6,000
Personal Whole Loan CLUB Certificates
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	309,037		667,582
Net gains (losses) recognized from loans securitized or sold	3,013		6,050
Fair value of senior securities and subordinated certificates received	15,481		33,307
Cash proceeds from loans securitized or sold	297,386		638,191
Cash proceeds from servicing and other administrative fees on loans securitized or sold	1,029		1,736
Cash proceeds for interest received on senior securities and subordinated certificates	$ 441		$ 852

Fair Value of Available for Sale Securities Retained upon Settlement

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Principal Derecognized from Loans Securitized or Sold during Period

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Proceeds from Servicing Rights Fees on Securitizations

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Transferor's Interests Retained in Transferred Financial Assets, Fair Value

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Cash received for dividends and interest on the entity's equity and debt investments during the current period.

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The cash inflow from the securitization of receivables for loans to consumers. Securitization is the structured process whereby interests in loans and other receivables are packaged, underwritten, and sold in the form of asset-backed securities.

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