v3.26.1
Share Data and Net Assets - Schedule of Changes in Net Assets (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Dec. 31, 2025
Jun. 30, 2025
Mar. 31, 2025
Dec. 31, 2024
Jun. 30, 2026
Jun. 30, 2025
Investment Company, Net Assets [Roll Forward]                
Beginning of period (in shares)     88,086,000       88,086,000  
Net assets at beginning of period $ 1,382,064 $ 1,436,187 $ 1,465,813 $ 1,475,113 $ 1,449,815 $ 1,487,811 $ 1,465,813 $ 1,487,811
Net investment income 32,521 34,362 36,703 33,481 39,055 44,302 103,586 116,838
Net unrealized appreciation (depreciation) 48,210 (39,338) (32,418) 18,572 (82,023) (19,614) (23,500) (83,100)
Net realized gains (losses) (49,539) (13,610) 1,342 (13,432) 6,705 (17,310) (61,800) (24,000)
(Provision) benefit for taxes on realized and unrealized gains (losses) (252) (303) (19) (269) 14 (139) (574) (394)
Distributions to stockholders (29,949) (35,234) (35,234) (36,996) (41,400) (45,235) $ (100,417) $ (123,631)
Issuance of common stock under dividend reinvestment plan (in shares)             275,776,000 639,964,000
Issuance of common stock under dividend reinvestment plan 1,082 1,140 1,137 3,751 4,289 1,455 $ 3,359 $ 9,495
Repurchase of common stock under dividend reinvestment plan (1,082) (1,140) (1,137) (3,751) (4,289) (1,455)    
Issuance of common stock in private placement 0     0 100,000   0 100,000
Issuance of common stock in connection with the "at the market" offering $ 0     0 2,947   $ 0 2,947
End of period (in shares) 88,086,000           88,086,000  
Net assets at end of period $ 1,383,055 $ 1,382,064 $ 1,436,187 $ 1,476,469 $ 1,475,113 $ 1,449,815 $ 1,383,055 $ 1,476,469
Common Stock                
Investment Company, Net Assets [Roll Forward]                
Beginning of period (in shares) 88,086,000 88,086,000 88,086,000 88,086,000 82,245,000 82,245,000 88,086,000 82,245,000
Net assets at beginning of period $ 881 $ 881 $ 881 $ 881 $ 822 $ 822 $ 881 $ 822
Issuance of common stock under dividend reinvestment plan (in shares) 88,000 98,000 89,000 269,000 276,000 95,000    
Issuance of common stock under dividend reinvestment plan $ 1 $ 1 $ 1 $ 3 $ 3 $ 1    
Repurchase of common stock under dividend reinvestment plan (in shares) (88,000) (98,000) (89,000) (269,000) (276,000) (95,000)    
Repurchase of common stock under dividend reinvestment plan $ (1) $ (1) $ (1) $ (3) $ (3) $ (1)    
Issuance of common stock in a private placement (in shares)         5,672,000      
Issuance of common stock in private placement         $ 57      
Issuance of common stock in connection with the "at the market" offering (in shares)         169,000      
Issuance of common stock in connection with the "at the market" offering         $ 2      
End of period (in shares) 88,086,000 88,086,000 88,086,000 88,086,000 88,086,000 82,245,000 88,086,000 88,086,000
Net assets at end of period $ 881 $ 881 $ 881 $ 881 $ 881 $ 822 $ 881 $ 881
Additional paid-in-capital                
Investment Company, Net Assets [Roll Forward]                
Net assets at beginning of period 2,350,075 2,350,075 2,350,075 2,367,337 2,264,449 2,264,449 2,350,075 2,264,449
Issuance of common stock under dividend reinvestment plan 1,081 1,139 1,136 3,748 4,286 1,454    
Repurchase of common stock under dividend reinvestment plan (1,081) (1,139) (1,136) (3,748) (4,286) (1,454)    
Issuance of common stock in private placement         99,943      
Issuance of common stock in connection with the "at the market" offering         2,945      
Net assets at end of period 2,350,075 2,350,075 2,350,075 2,367,337 2,367,337 2,264,449 2,350,075 2,367,337
Accumulated Overdistributed Earnings                
Investment Company, Net Assets [Roll Forward]                
Net assets at beginning of period (968,892) (914,769) (885,143) (893,105) (815,456) (777,460) (885,143) (777,460)
Net investment income 32,521 34,362 36,703 33,481 39,055 44,302    
Net unrealized appreciation (depreciation) 48,210 (39,338) (32,418) 18,572 (82,023) (19,614)    
Net realized gains (losses) (49,539) (13,610) 1,342 (13,432) 6,705 (17,310)    
(Provision) benefit for taxes on realized and unrealized gains (losses) (252) (303) (19) (269) 14 (139)    
Distributions to stockholders (29,949) (35,234) (35,234) (36,996) (41,400) (45,235)    
Net assets at end of period $ (967,901) $ (968,892) $ (914,769) $ (891,749) $ (893,105) $ (815,456) $ (967,901) $ (891,749)