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Loans and Allowance for Loan Losses - Summary of Aging of Loans (Parenthetical) (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Receivables [Abstract] |  |
Loan premiums | $ 2,717 | $ 5,758
Capitalized loan origination costs | $ 21,345 | $ 18,403

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- Definition Capitalized Loan Origination Costs + References No definition available. + Details
Name: | mfin_CapitalizedLoanOriginationCosts
Namespace Prefix: | mfin_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount of unearned premiums on outstanding advances made and reported by Federal Home Loan Bank (FHLBank). + References No definition available. + Details
Name: | us-gaap_FederalHomeLoanBankAdvancesPremium
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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