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Long-Term Debt - Schedule of Carrying Amounts of Consolidated VIE's Assets and Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash	$ 694		$ 3,657	$ 2,799		$ 5,230
Finance receivables	973,434		932,243	847,238
Allowance for credit losses	(57,200)	$ (56,400)	(58,300)	(48,450)	$ (47,750)	(48,910)
Restricted cash	41,803		46,484	$ 26,356		$ 16,787
Other assets	10,488		8,375
Total assets	1,019,316		956,395
Liabilities
Net long-term debt	681,953		651,349
Accounts payable and accrued expenses	19,690		25,138
Total liabilities	729,097		677,234
Variable Interest Entity, Primary Beneficiary [Member]
Assets
Cash	167		168
Finance receivables	356,679		342,481
Allowance for credit losses	(17,406)		(18,378)
Restricted cash	34,268		39,361
Other assets	129		75
Total assets	373,837		363,707
Liabilities
Net long-term debt	337,776		324,879
Accounts payable and accrued expenses	83		25
Total liabilities	$ 337,859		$ 324,904