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Finance Receivables, Credit Quality Information, and Allowance for Credit Losses - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 12 Months Ended
Sep. 30, 2018
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]        
Increase (decrease) in provision for credit losses   $ 23,343 $ 19,515  
Impaired finance receivables as a percentage of total finance receivables   3.20%   2.90%
Uncollectible Receivables [Member] | Hurricanes [Member]        
Financing Receivable, Allowance for Credit Losses [Line Items]        
Increase (decrease) in provision for credit losses $ 3,900 $ 2,000