Fair Value Measurements - Fair value measurements of investments and foreign currency forward contracts, by major class according to the fair value hierarchy (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Fair Value Measurements
Total investments	$ 1,422,873	$ 1,362,488
Recurring
Fair Value Measurements
Total investments	1,543,910	1,468,996
Foreign currency forward contracts asset (liability)	1,409	1,296
Recurring | Senior Secured Loans
Fair Value Measurements
Total investments	1,320,148	1,250,788
Recurring | Unitranche Secured Loans
Fair Value Measurements
Total investments	128,380	127,378
Recurring | Junior Secured Loans
Fair Value Measurements
Total investments	44,633	44,469
Recurring | Equity Securities
Fair Value Measurements
Total investments	50,749	46,361
Recurring | Level 1
Fair Value Measurements
Total investments	52	34
Recurring | Level 1 | Equity Securities
Fair Value Measurements
Total investments	52	34
Recurring | Level 2
Fair Value Measurements
Foreign currency forward contracts asset (liability)	1,409	1,296
Recurring | Level 3
Fair Value Measurements
Total investments	1,543,858	1,468,962
Recurring | Level 3 | Senior Secured Loans
Fair Value Measurements
Total investments	1,320,148	1,250,788
Recurring | Level 3 | Unitranche Secured Loans
Fair Value Measurements
Total investments	128,380	127,378
Recurring | Level 3 | Junior Secured Loans
Fair Value Measurements
Total investments	44,633	44,469
Recurring | Level 3 | Equity Securities
Fair Value Measurements
Total investments	$ 50,697	$ 46,327