CONSOLIDATED SCHEDULE OF INVESTMENTS (Parenthetical) (unaudited) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2026	Dec. 31, 2025
Aggregate gross unrealized gain of federal income tax	$ 26,955	$ 39,682
Aggregate gross unrealized loss of federal income tax	357,709	270,079
Aggregate net unrealized loss of federal income tax	330,754	230,397
Aggregate cost of federal income tax	$ 3,101,096	$ 3,398,235
Percentage of non-qualifying assets	7.70%	8.80%
Prime Rate
Investment reference rate percentage	6.75%	6.75%
SONIA
Investment reference rate percentage	3.73%	3.73%
1 Month SOFR
Investment reference rate percentage	3.65%	3.69%
3 Month SOFR
Investment reference rate percentage	3.73%	3.65%
6 Month SOFR
Investment reference rate percentage	3.85%	3.57%
12 Month SOFR
Investment reference rate percentage	3.99%	3.41%
1 Month CORRA
Investment reference rate percentage	2.28%	2.26%
3 Month CORRA
Investment reference rate percentage		2.26%
3 month EURIBOR
Investment reference rate percentage	2.32%	2.03%
6 Months EURIBOR
Investment reference rate percentage	2.57%	2.11%
Minimum
Percentage of qualifying assets	70.00%	70.00%
Affiliated Investments
Ownership percentage of outstanding voting securities of investment	5.00%	5.00%
Affiliated Investments \| Minimum
Investment, ownership percentage	25.00%	25.00%
Controlled Investments \| Minimum
Ownership percentage of outstanding voting securities of investment	25.00%	25.00%
Controlled Investments \| Maximum
Investment, ownership percentage	25.00%	25.00%
Restricted Securities
Restricted securities fair value	$ 146,564	$ 131,042
Restricted securities percent of net assets	13.00%	10.00%
Golden Bear 2016-R, LLC
Investment, ownership percentage	100.00%	100.00%
ChyronHego Corporation
Investment, ownership percentage	93.14%	87.00%
Merx Aviation Finance, LLC
Investment, ownership percentage	100.00%	100.00%
AIC SPV Holdings II, LLC
Economic ownership percentage	14.25%	14.25%
Auto Pool 2023
Investment, ownership percentage	22.50%	22.50%

Economic ownership percentage.

No definition available.

Name:	mfic_EconomicOwnershipPercentage
Namespace Prefix:	mfic_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Investment reference rate percentage.

+ References

No definition available.

+ Details

Name:	mfic_InvestmentReferenceRatePercentage
Namespace Prefix:	mfic_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Ownership percentage of outstanding voting securities of investment.

+ References

No definition available.

+ Details

Name:	mfic_OwnershipPercentageOfOutstandingVotingSecuritiesOfInvestment
Namespace Prefix:	mfic_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of equity ownership interest.

+ References

No definition available.

+ Details

Name:	mfic_PercentageOfEquityOwnershipInterest
Namespace Prefix:	mfic_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of non qualifying assets representing company total assets.

+ References

No definition available.

+ Details

Name:	mfic_PercentageOfNonQualifyingAssetsRepresentingCompanyTotalAssets
Namespace Prefix:	mfic_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of qualifying assets representing company total assets.

+ References

No definition available.

+ Details

Name:	mfic_PercentageOfQualifyingAssetsRepresentingCompanyTotalAssets
Namespace Prefix:	mfic_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate value of all restricted investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12(Column C)(Footnote 8)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-12B(Column C)(Footnote 11)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14(Column F)(Footnote 5)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 210
-Name Accounting Standards Codification
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477220/954-210-45-4

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478600/954-210-50-2

+ Details

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

- Definition

The percent of net assets of the aggregate value of all restricted investments.

+ References

+ Details

Name:	us-gaap_RestrictedInvestmentsPercentOfNetAssets
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cost of investment for federal income tax purpose.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(h)(2)(iv))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3

+ Details

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

- Definition

Amount of cumulative increase in investment from unrealized gain when value exceeds cost for federal income tax purpose.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(h)(2)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3

+ Details

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

- Definition

Amount of cumulative decrease in investment from unrealized loss when cost for federal income tax purpose exceeds value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(h)(2)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3

+ Details

Name:	us-gaap_TaxBasisOfInvestmentsGrossUnrealizedDepreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of cumulative increase (decrease) in investment from unrealized gain (loss) when value exceeds (is less than) cost for federal income tax purpose.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(h)(2)(iii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479886/946-10-S99-3

+ Details

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

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_SONIAInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_OneMonthSecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_ThreeMonthsSecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_SixMonthsSecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_TwelveMonthsSecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_OneMonthCorraInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_ThreeMonthCORRAInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_ThreeMonthsEuriborInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=mfic_SixMonthsEuriborInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=mfic_AffiliatedInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=mfic_ControlledInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=mfic_RestrictedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mfic_GoldenBear2016RLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mfic_ChyronHegoCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mfic_MerxAviationFinanceLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mfic_AICSPVHoldingsIILLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mfic_AutoPoolMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: