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Summary of Significant Accounting Policies - Concentrations of Portfolio Company Values Compared to the Fair Value of the Corporation's Total Investment Portfolio (Details) | 9 Months Ended | 12 Months Ended
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Sep. 30, 2025 | Dec. 31, 2024
Tilson |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio |  | 16.00%
Seybert's |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio |  | 11.00%
FSS |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio | 10.00% | 10.00%
All About People |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio | 9.00% |
EFINEA |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio | 11.00% |
Mattison |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio |  | 8.00%
First Coast Mulch |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio | 9.00% |
Caitec |  |
Concentration Risk [Line Items] |  |
Concentration risk investment portfolio | 11.00% | 6.00%

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