Fair Value of Assets and Liabilities - Loans, Loan Servicing Rights, Related Notes and Certificates (Detail) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment	[1]	$ 1,079,315	$ 1,883,251
Loans held for investment by the Company	[1]	43,693	2,583
Loans held for sale by the Company	[1]	722,355	840,021
Securities available for sale at fair value		270,927	170,469
Servicing assets		89,680	64,006
Total assets		2,205,970	2,960,330
Notes, certificates and secured borrowings	[1]	1,081,466	1,905,875
Payable to securitization note and certificate holders		40,610
Loan trailing fee liability		11,099	10,010
Total liabilities		1,133,175	1,915,885
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 securitization note and certificate holders		0
Loan trailing fee liability		0	0
Total liabilities		0	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		160,131	110,190
Servicing assets		0	0
Total assets		160,131	110,190
Notes, certificates and secured borrowings		0	0
Payable to securitization note and certificate holders		0
Loan trailing fee liability		0	0
Total liabilities		0	0
Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for investment		1,079,315	1,883,251
Loans held for investment by the Company		43,693	2,583
Loans held for sale by the Company		722,355	840,021
Securities available for sale at fair value		110,796	60,279
Servicing assets		89,680	64,006
Total assets		2,045,839	2,850,140
Notes, certificates and secured borrowings		1,081,466	1,905,875
Payable to securitization note and certificate holders		40,610
Loan trailing fee liability		11,099	10,010
Total liabilities		1,133,175	1,915,885
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		130,429	68,338
Asset-backed senior securities and subordinated securities | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Asset-backed senior securities and subordinated securities | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		109,339	56,489
Asset-backed senior securities and subordinated securities | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		21,090	11,849
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		89,706	48,430
CLUB Certificate asset-backed securities | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
CLUB Certificate asset-backed securities | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
CLUB Certificate asset-backed securities | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		89,706	48,430
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		14,343	17,328
Corporate debt securities | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Corporate debt securities | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		14,343	17,328
Corporate debt securities | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		13,100	14,929
Certificates of deposit | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			0
Certificates of deposit | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		13,100	14,929
Certificates of deposit | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		12,080	11,225
Other asset-backed securities | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Other asset-backed securities | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		12,080	11,225
Other asset-backed securities | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		9,274	9,720
Commercial paper | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
Commercial paper | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		9,274	9,720
Commercial paper | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0	0
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
U.S. agency securities | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		0
U.S. agency securities | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		1,995
U.S. agency securities | Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value		$ 0
Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			499
Other securities | Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			0
Other securities | Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale at fair value			499
Other securities | Level 3 Inputs
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.