Fair Value of Assets and Liabilities - Loans, Loan Servicing Rights, Related Notes and Certificates (Detail) - USD ($) $ in Thousands		Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment	[1]	$ 785,228	$ 1,079,315
Loans held for investment by the Company	[1]	65,557	43,693
Loans held for sale by the Company	[1]	587,093	722,355
Securities available for sale at fair value		221,930	270,927
Servicing assets		65,515	89,680
Total assets		1,725,323	2,205,970
Notes, certificates and secured borrowings	[1]	785,928	1,081,466
Payable to Structured Program note and certificate holders	[1]	193,034	40,610
Deferred revenue		4,538
Loan trailing fee liability		9,213	11,099
Total liabilities		992,713	1,133,175
Asset-backed senior securities and subordinated securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		113,572	130,429
CLUB Certificate asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		76,634	89,706
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		8,532	14,343
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		6,700	13,100
Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		8,199	12,080
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		8,293	9,274
U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			1,995
Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment		0	0
Loans held for investment by the Company		0	0
Loans held for sale by the Company		0	0
Securities available for sale at fair value		0	0
Servicing assets		0	0
Total assets		0	0
Notes, certificates and secured borrowings		0	0
Payable to Structured Program note and certificate holders		0	0
Deferred revenue		0
Loan trailing fee liability		0	0
Total liabilities		0	0
Level 1 Inputs | Asset-backed senior securities and subordinated securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 1 Inputs | CLUB Certificate asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 1 Inputs | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 1 Inputs | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 1 Inputs | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 1 Inputs | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 1 Inputs | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			0
Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment		0	0
Loans held for investment by the Company		0	0
Loans held for sale by the Company		0	0
Securities available for sale at fair value		126,340	160,131
Servicing assets		0	0
Total assets		126,340	160,131
Notes, certificates and secured borrowings		0	0
Payable to Structured Program note and certificate holders		0	0
Deferred revenue		0
Loan trailing fee liability		0	0
Total liabilities		0	0
Level 2 Inputs | Asset-backed senior securities and subordinated securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		94,616	109,339
Level 2 Inputs | CLUB Certificate asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 2 Inputs | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		8,532	14,343
Level 2 Inputs | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		6,700	13,100
Level 2 Inputs | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		8,199	12,080
Level 2 Inputs | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		8,293	9,274
Level 2 Inputs | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			1,995
Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment		785,228	1,079,315
Loans held for investment by the Company		65,557	43,693
Loans held for sale by the Company		587,093	722,355
Securities available for sale at fair value		95,590	110,796
Servicing assets		65,515	89,680
Total assets		1,598,983	2,045,839
Notes, certificates and secured borrowings		785,928	1,081,466
Payable to Structured Program note and certificate holders		193,034	40,610
Deferred revenue		4,538
Loan trailing fee liability		9,213	11,099
Total liabilities		992,713	1,133,175
Level 3 Inputs | Asset-backed senior securities and subordinated securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		18,956	21,090
Level 3 Inputs | CLUB Certificate asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		76,634	89,706
Level 3 Inputs | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 3 Inputs | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Level 3 Inputs | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			0
Level 3 Inputs | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		$ 0	0
Level 3 Inputs | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			$ 0

[1] Includes amounts in consolidated variable interest entities (VIEs) presented separately in the table below.