Securitizations and Variable Interest Entities - Summary of Personal Whole Loan Securitizations and Sales (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 06, 2017
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Fair value of senior securities and subordinated certificates retained upon settlement (1)	$ 117,573	$ 287,137
Cash proceeds from loans securitized or sold	313,486	0	$ 0
Personal Whole Loan Securitizations
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	999,128	0	0	$ 368,000
Net gains (losses) recognized from loans securitized or sold	4,987	0	0
Fair value of senior securities and subordinated certificates retained upon settlement (1)	53,154	0	0
Cash proceeds from loans securitized or sold	812,851	0	0
Cash proceeds from subordinated certificates sold	6,300	0	0
Cash proceeds from servicing and other administrative fees on loans securitized or sold	2,641	0	0
Cash proceeds for interest received on senior securities and subordinated certificates	300	0	0
Personal Whole Loan Club Certificate
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	37,779	0	0
Net gains (losses) recognized from loans securitized or sold	(177)	0	0
Fair value of senior securities and subordinated certificates retained upon settlement (1)	1,802	0	0
Cash proceeds from loans securitized or sold	34,575	0	0
Cash proceeds from subordinated certificates sold	0	0	0
Cash proceeds from servicing and other administrative fees on loans securitized or sold	21	0	0
Cash proceeds for interest received on senior securities and subordinated certificates	5	$ 0	$ 0
Senior Securities \| Personal Whole Loan Securitizations
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Interests retained by the Company	43,417
Subordinated residual certificates \| Personal Whole Loan Securitizations
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Interests retained by the Company	$ 9,737

Proceeds from Servicing Rights Fees on Securitizations

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Proceeds from Subordinated Trust Certificates

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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A gain (loss) realized on a transfer, accounted for as a sale, of all or a portion of financial assets in which the transferor surrenders control and receives consideration other than a beneficial interest in the assets transferred. Reflects the amount of sales proceeds in excess of, or deficient from, the sum of the carrying amounts of transferred financial assets plus transaction costs.

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The carrying amount (fair value) as of the balance sheet date of the transferor's interests in transferred financial assets (typically securitized receivables, generally not involved in the collection of principal) following transfer of significant portions of such financial instruments to other parties. Such interests could be ancillary cash flows and interest-only strips.

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This is the principal amount outstanding for securitized loans only (across all types of loans).

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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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