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Disclosure About Fair Value of Financial Instruments - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017
Fair Value Disclosures [Abstract] |
Turnover rate of loan portfolio | 1.3

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- Definition The annual turnover of the finance receivables in the portfolio. + References No definition available. + Details
Name: | rm_FinanceReceivablePortfolioTurnoverRate
Namespace Prefix: | rm_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration