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, 2023	Dec. 31, 2022
Tilson
Accounting Policies [Line Items]
Concentration risk investment portfolio	15.00%	17.00%
Seybert's
Accounting Policies [Line Items]
Concentration risk investment portfolio	9.00%	10.00%
Sciaps
Accounting Policies [Line Items]
Concentration risk investment portfolio	8.00%	8.00%
ITA
Accounting Policies [Line Items]
Concentration risk investment portfolio	8.00%
DSD
Accounting Policies [Line Items]
Concentration risk investment portfolio	7.00%	8.00%
Caitec
Accounting Policies [Line Items]
Concentration risk investment portfolio		6.00%