Summary of Significant Accounting Policies - Concentrations of Portfolio Company Values Compared to the Fair Value of the Corporation's Total Investment Portfolio (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Tilson
Accounting Policies [Line Items]
Concentration risk investment portfolio	13.00%	14.00%
FSS
Accounting Policies [Line Items]
Concentration risk investment portfolio	9.00%	10.00%
Seybert's
Accounting Policies [Line Items]
Concentration risk investment portfolio	9.00%	8.00%
Mattison
Accounting Policies [Line Items]
Concentration risk investment portfolio	7.00%
Sciaps
Accounting Policies [Line Items]
Concentration risk investment portfolio	6.00%	7.00%
INEA
Accounting Policies [Line Items]
Concentration risk investment portfolio		6.00%