Finance Receivables - Special Product (New Neighbor Guaranty program) - Additional Information (Detail) - Special Product [Member]	12 Months Ended
Dec. 31, 2017 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Delinquent assessments maximum due period purchases basis	48 months
Maximum future contingent payments	$ 461,000

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration