Finance Receivables - Special Product (New Neighbor Guaranty program) - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Special Product [Member]
Accounts Notes And Loans Receivable [Line Items]
Delinquent assessments maximum due period purchases basis	48 months
Maximum future contingent payments		$ 249,000
New Neighbor Guaranty (NNG) [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance for credit losses	$ 20,000	$ 41,000