v3.23.3
Portfolio Investments - Summarized Balance Sheet Information (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
Investment Company, Nonconsolidated Subsidiary [Line Items]      
Investments at fair value $ 2,892,420 $ 2,494,111  
Cash and cash equivalents 136,450 23,528 $ 29,334
Restricted cash 9,089 2,836 $ 2,301
Other assets 1,681 1,665  
Total assets 3,217,839 2,646,313  
Credit facilities payable 710,000 700,000  
Secured borrowings 18,106 0  
Due to affiliate 4,310 3,180  
Total liabilities 1,702,075 1,400,750  
Total liabilities and net assets 3,217,839 2,646,313  
Investment owned, at cost 3,044,119 2,617,754  
SLF JV I      
Investment Company, Nonconsolidated Subsidiary [Line Items]      
Investments at fair value 322,179 359,625  
Cash and cash equivalents 31,950 14,274  
Restricted cash 2,987 5,642  
Other assets 18,988 5,686  
Total assets 376,104 385,227  
Credit facilities payable 149,000 230,000  
Secured borrowings 38,845 0  
Notes payable at fair value 128,750 110,000  
Due to affiliate 26,630 21,539  
Total liabilities 343,225 361,539  
Members' equity 32,879 23,688  
Total liabilities and net assets 376,104 385,227  
Investment owned, at cost 331,808 382,673  
Net proceeds 128,750 110,000  
OCSI Glick JV LLC      
Investment Company, Nonconsolidated Subsidiary [Line Items]      
Investments at fair value 123,343 133,144  
Cash and cash equivalents 12,119 7,021  
Restricted cash 184 1,788  
Other assets 5,521 4,855  
Total assets 141,167 146,808  
Credit facilities payable 53,000 82,082  
Notes payable at fair value 57,201 57,463  
Due to affiliate 12,860 7,263  
Total liabilities 141,167 146,808  
Members' equity 0 0  
Total liabilities and net assets 141,167 146,808  
Investment owned, at cost 127,788 140,083  
Net proceeds $ 66,685 $ 68,185