Fair Value of Assets and Liabilities - Additional Information about Servicing Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Servicing Assets, Changes in fair value due to:
Fair value at beginning of period			$ 56,347
Fair value at end of period	$ 63,573		63,573
Fair Value, Measurements, Recurring
Servicing Assets, Changes in fair value due to:
Fair value at beginning of period	58,728	$ 65,515	56,347	$ 89,680
Issuances	21,071	7,783	46,274	27,119
Change in fair value, included in Marketplace revenue	(14,984)	(13,376)	(39,584)	(48,046)
Other net changes included in Deferred revenue	(1,242)	(384)	536	(9,215)
Fair value at end of period	63,573	59,538	63,573	59,538
Asset-backed subordinated securities related to Company-sponsored Structured Program transactions
Servicing Liabilities, Changes in fair value due to:
Fair value at beginning of period	45,918	95,590	66,654	110,796
Additions	488	446	1,445	26,458
Redemptions	(1,525)	(426)	(3,749)	(802)
Transfers	0	(517)	0	(517)
Cash received	(12,869)	(20,297)	(42,683)	(54,371)
Change in unrealized gain	2,110	3,413	6,968	288
Accrued interest	1,369	1,823	4,064	5,649
Reversal of (impairment on) securities available for sale	495	3,669	3,287	(3,800)
Fair value at end of period	$ 35,986	$ 83,701	$ 35,986	$ 83,701

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Accrued Interest

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Provision for Credit Recovery (Loss) Expense

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Retirements

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Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

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Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Amount of increase (decrease) in fair value from changes in the inputs, assumptions, or model used to calculate the fair value of the contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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Amount of increase (decrease) in fair value from changes classified as other for a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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