Organization of Medallion Financial Corp. and its Subsidiaries - Additional Information (Detail)	6 Months Ended
Jun. 30, 2020 USD ($) Medallion	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)
Subsidiary or Equity Method Investee [Line Items]
Purchase price for City of Chicago taxi medallions out of foreclosure	$ 8,689,000
Number of medallions purchased out of foreclosure \| Medallion	159
Net realizable value of medallions	$ 3,091,000	$ 3,091,000	$ 3,091,000
Medallion Financing Trust I [Member]
Subsidiary or Equity Method Investee [Line Items]
Aggregate assets of trust	$ 36,083,000

Number of medallions.

No definition available.

Name:	mfin_NumberOfMedallions
Namespace Prefix:	mfin_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(b))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Name:	us-gaap_AssetsHeldInTrust
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of reorganization value related to estimated net realizable value of asset dispositions. Reorganization value is the amount attributed to the reconstituted entity, as well as the expected net realizable value of those assets that will be disposed before reconstitution occurs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 05
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=49179835&loc=d3e54813-112758

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56239-112766

+ Details

Name:	us-gaap_ReorganizationValueNetRealizableValueOfAssetDispositions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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

- Details

Name:	srt_ConsolidatedEntitiesAxis=mfin_MedallionFinancingTrustIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: