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Financial Highlights - Summary of Information about Senior Securities (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Jul. 27, 2022
Oct. 27, 2021
Dec. 11, 2020
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Convertible Notes $ 48,916   $ 48,757            
Total 737,500 $ 616,000              
2025 Notes                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Total             $ 182,500    
KeyBank Credit Facility                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility 190,000   213,000         $ 350,000  
Senior Securities                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility 737,500   645,500 $ 620,000 $ 466,000        
Asset Coverage per Unit 1,849   1,947 1,741 1,958        
Senior Securities | 2025 Notes                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility   182,500 182,500 182,500 125,000 $ 125,000      
Asset Coverage per Unit 1,849   1,947 1,741 1,958 1,770      
Average Market Value per Unit 1,011   1,006 1,006          
Senior Securities | Convertible Notes                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility 50,000   50,000 50,000 50,000       $ 50,000
Asset Coverage per Unit 1,849 $ 1,947   1,741 1,958 1,770      
Senior Securities | August 2026 Notes                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility 125,000   125,000 125,000 125,000        
Asset Coverage per Unit 1,849   1,947   1,741 1,958      
Senior Securities | December 2026 Notes                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility 75,000   75,000 75,000   75,000      
Asset Coverage per Unit 1,849   1,947 1,741 1,958        
Senior Securities | March 2029 Notes                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility 115,000                
Asset Coverage per Unit 1,849                
Senior Securities | Credit Suisse Credit Facility                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility         10,000 135,000      
Asset Coverage per Unit         1,958 $ 1,770      
Senior Securities | KeyBank Credit Facility                  
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]                  
Credit facility 190,000   213,000 187,500 81,000        
Asset Coverage per Unit $ 1,849   $ 1,947 $ 1,741 $ 1,958