Finance Receivables - Summary of contracts and direct loans included in finance receivables (Details) - Finance receivables - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Accounts Notes And Loans Receivable [Line Items]
Allowance for credit losses	$ (11,469)	$ (11,248)	$ (11,162)	$ (13,502)	$ (16,112)	$ (16,932)
Contracts and direct loans
Accounts Notes And Loans Receivable [Line Items]
Finance receivables	198,168		219,366	222,320
Accrued interest receivable	2,817		3,164	3,046
Unearned dealer discounts	(7,411)		(8,056)	(8,995)
Unearned insurance and fee commissions	(2,460)		(2,616)	(2,741)
Purchase price discount	(610)		(915)	(676)
Finance receivables, net of unearned	190,504		210,943	212,954
Allowance for credit losses	(11,469)		(11,162)	(13,502)
Finance receivables, net	$ 179,035		$ 199,781	$ 199,452