Quarterly report pursuant to Section 13 or 15(d)

Finance Receivables - Original Product - Schedule of Finance Receivables for Original Product (Detail)

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Finance Receivables - Original Product - Schedule of Finance Receivables for Original Product (Detail) - Original Product [Member]
9 Months Ended 12 Months Ended
Sep. 30, 2018
USD ($)
Unit
Dec. 31, 2017
USD ($)
Unit
Accounts Notes And Loans Receivable [Line Items]    
Finance receivables outstanding $ 645,000 $ 832,000
Reserve for credit losses (180,000) (194,000)
Finance receivables, net $ 465,000 $ 638,000
Number of active units with delinquent assessments | Unit 896 1,162
Amount of outstanding interest and late fees on active units $ 13,264,000 $ 14,600,000
Funded During The Current Year [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Finance receivables outstanding 45,000 118,000
1-2 Years Outstanding [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Finance receivables outstanding 51,000 38,000
2-3 Years Outstanding [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Finance receivables outstanding 25,000 12,000
3-4 Years Outstanding [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Finance receivables outstanding 8,000 24,000
Greater Than 4 Years Outstanding [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Finance receivables outstanding $ 516,000 $ 640,000