v3.23.3
Share Data and Net Assets - Schedule of Changes in Net Assets (Details) - USD ($)
$ in Thousands
 12 Months Ended
Jan. 23, 2023
Mar. 19, 2021
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
Investment Company, Net Assets [Roll Forward]          
Beginning of period (shares)     61,125,000    
Net assets at beginning of period     $ 1,245,563 [1] $ 1,312,823 $ 914,879
Net investment income     180,697 148,621 97,106
Net unrealized appreciation (depreciation)     (28,555) (136,248) 114,519
Net realized gains (losses)     (33,155) 17,179 26,420
(Provision) benefit for taxes on realized and unrealized gains (losses)     (1,656) (329) (785)
Net increase (decrease) in net assets from stockholder transactions     (185,900) (118,657) (82,020)
Reclassification of additional paid-in capital         0
Issuance of common stock in connection with the OSI2 Merger (shares) 15,860,200 13,133,337      
Issuance of common stock in connection with mergers     334,034 0 242,704
Issuance of common stock in connection with the "at the market" offering     $ 1,300 $ 20,622 $ 0
Issuance of common stock under dividend reinvestment plan (shares)     297,336 165,651 112,573
Issuance of common stock under dividend reinvestment plan     $ 5,854 $ 3,409 $ 2,170
Repurchase of common stock under dividend reinvestment plan     $ (2,418) $ (1,857) (2,170)
End of period (shares)     77,225,000 61,125,000  
Net assets at end of period     $ 1,515,764 [1] $ 1,245,563 [1] $ 1,312,823
Common Stock          
Investment Company, Net Assets [Roll Forward]          
Beginning of period (shares)     61,125,000 60,120,000 46,987,000
Net assets at beginning of period     $ 611 $ 601 $ 470
Issuance of common stock in connection with the OSI2 Merger (shares)     15,860,000   13,133,000
Issuance of common stock in connection with mergers     $ 159   $ 131
Issuance of common stock in connection with the "at the market" offering (shares)     69,000 934,000  
Issuance of common stock in connection with the "at the market" offering     $ 1 $ 9  
Issuance of common stock under dividend reinvestment plan (shares)     297,000 166,000 113,000
Issuance of common stock under dividend reinvestment plan     $ 3 $ 2 $ 1
Repurchase of common stock under dividend reinvestment plan (shares)     (126,000) (95,000) (113,000)
Repurchase of common stock under dividend reinvestment plan     $ (2) $ (1) $ (1)
End of period (shares)     77,225,000 61,125,000 60,120,000
Net assets at end of period     $ 772 $ 611 $ 601
Additional paid-in-capital          
Investment Company, Net Assets [Roll Forward]          
Net assets at beginning of period     1,827,721 1,805,557 1,488,713
Reclassification of additional paid-in capital         74,271
Issuance of common stock in connection with mergers     333,875   242,573
Issuance of common stock in connection with the "at the market" offering     1,299 20,613  
Issuance of common stock under dividend reinvestment plan     5,851 3,407 2,169
Repurchase of common stock under dividend reinvestment plan     (2,416) (1,856) (2,169)
Net assets at end of period     2,166,330 1,827,721 1,805,557
Accumulated Overdistributed Earnings          
Investment Company, Net Assets [Roll Forward]          
Net assets at beginning of period     (582,769) (493,335) (574,304)
Net investment income     180,697 148,621 97,106
Net unrealized appreciation (depreciation)     (28,555) (136,248) 114,519
Net realized gains (losses)     (33,155) 17,179 26,420
(Provision) benefit for taxes on realized and unrealized gains (losses)     (1,656) (329) (785)
Net increase (decrease) in net assets from stockholder transactions     (185,900) (118,657) (82,020)
Reclassification of additional paid-in capital         (74,271)
Net assets at end of period     $ (651,338) $ (582,769) $ (493,335)
[1] As discussed in Note 2, the Company completed a 1-for-3 reverse stock split on January 20, 2023, effective as of the commencement of trading on January 23, 2023. The issued and outstanding shares and net asset value per share reflect the reverse stock split on a retroactive basis.