Finance Receivables - Original Product - Schedule of Finance Receivables for Original Product (Detail) - Original Product [Member]	12 Months Ended
	Dec. 31, 2017 USD ($) Unit	Dec. 31, 2016 USD ($) Unit
Accounts Notes And Loans Receivable [Line Items]
Finance receivables outstanding	$ 832,000	$ 1,036,000
Reserve for credit losses	(194,000)
Finance receivables, net	$ 638,000	$ 1,036,000
Number of active units with delinquent assessments | Unit	1,162	1,490
Amount of outstanding interest and late fees on active units	$ 14,600,000	$ 18,000,000
Funded During The Current Year [Member]
Accounts Notes And Loans Receivable [Line Items]
Finance receivables outstanding	118,000	80,000
1-2 Years Outstanding [Member]
Accounts Notes And Loans Receivable [Line Items]
Finance receivables outstanding	38,000	31,000
2-3 Years Outstanding [Member]
Accounts Notes And Loans Receivable [Line Items]
Finance receivables outstanding	12,000	37,000
3-4 Years Outstanding [Member]
Accounts Notes And Loans Receivable [Line Items]
Finance receivables outstanding	24,000	144,000
Greater Than 4 Years Outstanding [Member]
Accounts Notes And Loans Receivable [Line Items]
Finance receivables outstanding	$ 640,000	$ 744,000