Base amount considered for covenants.

No definition available.

Name:	mfic_BaseAmountConsideredForCovenants
Namespace Prefix:	mfic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Considered percentage of net proceeds from sale of equity interest for covenants calculation.

+ References

No definition available.

+ Details

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Namespace Prefix:	mfic_
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Balance Type:	na
Period Type:	duration

- Definition

Debt instrument fronting fees on letters of credit issued.

+ References

No definition available.

+ Details

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

- Definition

Debt instrument number of installment.

+ References

No definition available.

+ Details

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Namespace Prefix:	mfic_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Required assets coverage percentage.

+ References

No definition available.

+ Details

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

- Definition

Required indebtedness ratio for covenants.

+ References

No definition available.

+ Details

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Namespace Prefix:	mfic_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Required minimum percentage of equity to assets.

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the debt agreement requires the first payment to be made, in YYYY-MM-DD format.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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-SubTopic 20
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+ Details

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

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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

- Definition

Description of the frequency of the required periodic payments of interest, principal, or both, and the amount, if set, or a description of a formula upon which payment is based.

+ References

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

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Name:	us-gaap_VariableRateAxis=mfic_SterlingOvernightIndexAverageMember
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Balance Type:
Period Type:

- Details

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Balance Type:
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- Details

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Debt and Foreign Currency Transactions and Translations -- Additional Information (Details)			3 Months Ended	12 Months Ended
	Jul. 16, 2021 USD ($)	Mar. 03, 2015 USD ($)	Mar. 31, 2023 USD ($) Installment	Dec. 31, 2022 USD ($)	Nov. 19, 2022 USD ($)	Apr. 04, 2019	Apr. 04, 2018
Debt Instrument [Line Items]
Aggregate principal amount			$ 2,180,000,000	$ 2,238,829,000
Senior Secured Facility
Debt Instrument [Line Items]
Required assets coverage percentage						150.00%	200.00%
Final Maturity Date			Dec. 22, 2025	Dec. 22, 2025
Aggregate principal amount			$ 1,705,000,000	$ 1,763,829,000
Date of first required payment to repay			Dec. 22, 2024
Number of installment \| Installment			12
Frequency of payment and payment terms			Commencing December 22, 2024, the Company is required to repay, in twelve consecutive monthly installments of equal size, the outstanding amount under the Senior Secured Facility as of December 22, 2024.
Frequency of periodic payment			monthly
Commitment fee per annum			0.375%
Required minimum percentage of equity to assets			30.00%
Base amount considered for covenants			$ 705,000,000
Considered percentage of net proceeds from sale of equity interest for covenants			25.00%
Maximum borrowing capacity			$ 1,705,000,000	1,763,829,000	$ 1,810,000,000
Available remaining capacity			$ 655,436,000	$ 713,634,000
Senior Secured Facility \| LIBOR
Debt Instrument [Line Items]
Annual interest rate			2.00%
Senior Secured Facility \| SONIA
Debt Instrument [Line Items]
Annual interest rate			2.00%
2025 Notes
Debt Instrument [Line Items]
Final Maturity Date		Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025
Aggregate principal amount		$ 350,000,000	$ 350,000,000	$ 350,000,000
Date of first required payment to repay		Sep. 03, 2015
Frequency of payment and payment terms			The 2025 Notes will mature on March 3, 2025. Interest on the 2025 Notes is due semi-annually on March 3 and September 3, at an annual rate of 5.25%, commencing on September 3, 2015.
Frequency of periodic payment		semi-annually
Net proceeds from senior unsecured notes		$ 343,650,000
Annual interest rate		5.25%
2026 Notes
Debt Instrument [Line Items]
Final Maturity Date	Jul. 16, 2026		Jul. 16, 2026	Jul. 16, 2026
Aggregate principal amount	$ 125,000,000		$ 125,000,000	$ 125,000,000
Date of first required payment to repay	Jan. 16, 2022
Frequency of payment and payment terms			The 2026 Notes will mature on July 16, 2026. Interest on the 2026 Notes is due semi-annually on January 16 and July 16, at an annual rate of 4.50%, commencing on January 16, 2022.
Frequency of periodic payment	semi-annually
Net proceeds from senior unsecured notes	$ 122,965,000
Annual interest rate	4.50%
Maximum \| Senior Secured Facility
Debt Instrument [Line Items]
Fronting fees on letters of credit issued			2.25%
Maximum \| Senior Secured Facility \| LIBOR
Debt Instrument [Line Items]
Borrowing base interest rate			2.00%
Maximum \| Senior Secured Facility \| Alternate Base Rate
Debt Instrument [Line Items]
Borrowing base interest rate			1.00%
Minimum \| Senior Secured Facility
Debt Instrument [Line Items]
Required indebtedness ratio for covenants			1.5
Minimum \| Senior Secured Facility \| LIBOR
Debt Instrument [Line Items]
Borrowing base interest rate			1.75%
Minimum \| Senior Secured Facility \| Alternate Base Rate
Debt Instrument [Line Items]
Borrowing base interest rate			0.75%
Standby Letters of Credit \| Senior Secured Facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 150,000,000
Line of credit			$ 49,851,000	$ 37,692,000