Investments - SLP Schedule of Investments (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Open Forward Foreign Currency Contract [Line Items]
Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,136,466	$ 1,116,391	$ 1,100,006	$ 1,068,004
Interest Rate Floor One
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	1.00%	1.00%
Interest Rate Floor Two
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	0.75%	0.75%
Interest Rate Floor Three
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	0.50%	0.50%
Interest Rate Floor Four
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	0.00%	0.00%
Interest Rate Floor Five
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	0.25%	0.25%
Bain Capital Senior Loan Program, LLC
Open Forward Foreign Currency Contract [Line Items]
Equity, Including Portion Attributable to Noncontrolling Interest	$ 15,269	$ 23,042
Bain Capital Senior Loan Program, LLC | Interest Rate Floor One
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	1.00%	1.00%
Bain Capital Senior Loan Program, LLC | Interest Rate Floor Two
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	0.75%	0.75%
Bain Capital Senior Loan Program, LLC | Interest Rate Floor Three
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	0.50%	0.50%
Bain Capital Senior Loan Program, LLC | Interest Rate Floor Four
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	0.00%	0.00%
Bain Capital Senior Loan Program, LLC | Interest Rate Floor Five
Open Forward Foreign Currency Contract [Line Items]
Investment interest floor rate	1.50%	1.50%