XML 59 R48.htm IDEA: XBRL DOCUMENT
v3.25.3

FAIR VALUE HIERARCHY FOR INVESTMENTS—PORTFOLIO COMPOSITION - Percentage of Portfolio Investments by Industry Sector (Details) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2025 | Dec. 31, 2024
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 100.00% | 100.00%
Investment Owned, At Cost | Industry Concentration Risk | Electrical Equipment |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 8.80% | 4.60%
Investment Owned, At Cost | Industry Concentration Risk | Commercial Services & Supplies |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 7.90% | 7.60%
Investment Owned, At Cost | Industry Concentration Risk | Machinery |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 7.40% | 7.80%
Investment Owned, At Cost | Industry Concentration Risk | Professional Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 5.80% | 6.10%
Investment Owned, At Cost | Industry Concentration Risk | Internet Software & Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 5.20% | 7.20%
Investment Owned, At Cost | Industry Concentration Risk | Construction & Engineering |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 5.00% | 2.10%
Investment Owned, At Cost | Industry Concentration Risk | Distributors |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 4.80% | 4.30%
Investment Owned, At Cost | Industry Concentration Risk | Containers & Packaging |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 4.60% | 4.50%
Investment Owned, At Cost | Industry Concentration Risk | Diversified Consumer Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 4.60% | 5.20%
Investment Owned, At Cost | Industry Concentration Risk | IT Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 4.60% | 4.60%
Investment Owned, At Cost | Industry Concentration Risk | Chemicals |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 3.40% | 0.40%
Investment Owned, At Cost | Industry Concentration Risk | Leisure Equipment & Products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 3.30% | 3.50%
Investment Owned, At Cost | Industry Concentration Risk | Auto Components |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 3.00% | 1.70%
Investment Owned, At Cost | Industry Concentration Risk | Hotels, Restaurants & Leisure |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.80% | 2.80%
Investment Owned, At Cost | Industry Concentration Risk | Textiles, Apparel & Luxury Goods |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.70% | 2.80%
Investment Owned, At Cost | Industry Concentration Risk | Specialty Retail |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.50% | 2.00%
Investment Owned, At Cost | Industry Concentration Risk | Communications Equipment |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.30% | 2.90%
Investment Owned, At Cost | Industry Concentration Risk | Health Care Providers & Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.10% | 4.20%
Investment Owned, At Cost | Industry Concentration Risk | Computers & Peripherals |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.90% | 3.00%
Investment Owned, At Cost | Industry Concentration Risk | Software |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.70% | 1.60%
Investment Owned, At Cost | Industry Concentration Risk | Energy Equipment & Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.60% | 1.60%
Investment Owned, At Cost | Industry Concentration Risk | Marine |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.60% | 1.50%
Investment Owned, At Cost | Industry Concentration Risk | Internet & Catalog Retail |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.50% | 1.60%
Investment Owned, At Cost | Industry Concentration Risk | Household Products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.40% | 1.70%
Investment Owned, At Cost | Industry Concentration Risk | Food & Staples Retailing |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.30% | 1.60%
Investment Owned, At Cost | Industry Concentration Risk | Trading Companies & Distributors |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.30% | 1.30%
Investment Owned, At Cost | Industry Concentration Risk | Aerospace & Defense |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.20% | 1.70%
Investment Owned, At Cost | Industry Concentration Risk | Air Freight & Logistics |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.10% | 0.90%
Investment Owned, At Cost | Industry Concentration Risk | Diversified Financial Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.10% | 2.30%
Investment Owned, At Cost | Industry Concentration Risk | Media |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.00% | 1.20%
Investment Owned, At Cost | Industry Concentration Risk | Health Care Equipment & Supplies |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 0.60% | 1.10%
Investment Owned, At Cost | Industry Concentration Risk | Building Products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 0.40% | 2.20%
Investment Owned, At Cost | Industry Concentration Risk | Other |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.50% | 2.40%
Investment Owned, At Fair Value | Industry Concentration Risk | Electrical Equipment |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 9.00% | 4.70%
Investment Owned, At Fair Value | Industry Concentration Risk | Commercial Services & Supplies |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 7.40% | 6.60%
Investment Owned, At Fair Value | Industry Concentration Risk | Machinery |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 8.50% | 9.10%
Investment Owned, At Fair Value | Industry Concentration Risk | Professional Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 5.70% | 6.10%
Investment Owned, At Fair Value | Industry Concentration Risk | Internet Software & Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 3.80% | 6.30%
Investment Owned, At Fair Value | Industry Concentration Risk | Construction & Engineering |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 5.70% | 3.00%
Investment Owned, At Fair Value | Industry Concentration Risk | Distributors |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 5.50% | 4.30%
Investment Owned, At Fair Value | Industry Concentration Risk | Containers & Packaging |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 4.70% | 4.80%
Investment Owned, At Fair Value | Industry Concentration Risk | Diversified Consumer Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 5.10% | 6.00%
Investment Owned, At Fair Value | Industry Concentration Risk | IT Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 4.40% | 4.50%
Investment Owned, At Fair Value | Industry Concentration Risk | Chemicals |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 3.20% | 0.40%
Investment Owned, At Fair Value | Industry Concentration Risk | Leisure Equipment & Products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.60% | 2.90%
Investment Owned, At Fair Value | Industry Concentration Risk | Auto Components |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 3.00% | 1.70%
Investment Owned, At Fair Value | Industry Concentration Risk | Hotels, Restaurants & Leisure |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.80% | 2.00%
Investment Owned, At Fair Value | Industry Concentration Risk | Textiles, Apparel & Luxury Goods |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.50% | 2.60%
Investment Owned, At Fair Value | Industry Concentration Risk | Specialty Retail |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.30% | 2.20%
Investment Owned, At Fair Value | Industry Concentration Risk | Communications Equipment |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.30% | 1.40%
Investment Owned, At Fair Value | Industry Concentration Risk | Health Care Providers & Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.90% | 3.80%
Investment Owned, At Fair Value | Industry Concentration Risk | Computers & Peripherals |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 3.80% | 5.10%
Investment Owned, At Fair Value | Industry Concentration Risk | Software |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 2.10% | 2.10%
Investment Owned, At Fair Value | Industry Concentration Risk | Energy Equipment & Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.50% | 1.30%
Investment Owned, At Fair Value | Industry Concentration Risk | Marine |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.50% | 1.40%
Investment Owned, At Fair Value | Industry Concentration Risk | Internet & Catalog Retail |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 0.90% | 1.40%
Investment Owned, At Fair Value | Industry Concentration Risk | Household Products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.40% | 1.80%
Investment Owned, At Fair Value | Industry Concentration Risk | Food & Staples Retailing |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.10% | 1.30%
Investment Owned, At Fair Value | Industry Concentration Risk | Trading Companies & Distributors |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.20% | 1.30%
Investment Owned, At Fair Value | Industry Concentration Risk | Aerospace & Defense |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.20% | 1.70%
Investment Owned, At Fair Value | Industry Concentration Risk | Air Freight & Logistics |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.50% | 1.40%
Investment Owned, At Fair Value | Industry Concentration Risk | Diversified Financial Services |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.10% | 2.30%
Investment Owned, At Fair Value | Industry Concentration Risk | Media |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.00% | 1.50%
Investment Owned, At Fair Value | Industry Concentration Risk | Building Products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 0.50% | 2.30%
Investment Owned, At Fair Value | Industry Concentration Risk | Other |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Concentration risk, percentage (as a percent) | 1.80% | 2.70%

X
- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 42 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-42 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 275 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482861/275-10-50-18 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 275 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482861/275-10-50-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 275 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 20 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482861/275-10-50-20 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 275 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482861/275-10-50-18 Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 275 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482861/275-10-50-18 Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 275 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482861/275-10-50-18 + Details
Name: | us-gaap_ConcentrationRiskPercentage1
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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 Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 805 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479328/805-10-50-8 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 805 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 43 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479303/805-10-55-43 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 103 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-103 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=msif_InvestmentOwnedAtCostMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=msif_IndustryConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_ElectricalEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_CommercialServicesAndSuppliesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_MachineryMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_ProfessionalServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_InternetSoftwareAndServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_ConstructionAndEngineeringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_DistributorsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_ContainersAndPackagingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_DiversifiedConsumerServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_ITServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_ChemicalsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_LeisureEquipmentAndProductsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_AutoComponentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_HotelsRestaurantsAndLeisureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_TextilesApparelAndLuxuryGoodsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_SpecialtyRetailMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_CommunicationsEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_HealthCareProvidersAndServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_ComputersAndPeripheralsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_SoftwareMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_EnergyEquipmentAndServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_MarineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_InternetAndCatalogRetailMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_HouseholdProductsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_FoodAndStaplesRetailingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_TradingCompaniesAndDistributorsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_AerospaceAndDefenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_AirFreightAndLogisticsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_DiversifiedFinancialServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_MediaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_HealthCareEquipmentAndSuppliesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_BuildingProductsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=msif_OtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=msif_InvestmentOwnedAtFairValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |