Annual report pursuant to Section 13 and 15(d)

Investments - Schedule of Realized Gains and Losses and Changes in Unrealized Appreciation and Depreciation on Control and Affiliate investments (Details)

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Investments - Schedule of Realized Gains and Losses and Changes in Unrealized Appreciation and Depreciation on Control and Affiliate investments (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Schedule Of Investments [Line Items]      
Investments, at fair value: $ 3,248,046 $ 2,963,955  
Total fee income 26,243 14,430 $ 27,616
Total net change in unrealized appreciation (depreciation) 25,010 (85,063) 3,311
Control investments      
Schedule Of Investments [Line Items]      
Investments, at fair value: 115,004 76,458 73,504
Interest income 4,642 4,621 4,009
Total fee income 95 68 59
Total net change in unrealized appreciation (depreciation) 22,634 (278) (2,677)
Total net realized gain (loss) 0 0 0
Control investments | Coronado Aesthetics, LLC      
Schedule Of Investments [Line Items]      
Investments, at fair value: 262 319 565
Interest income 0 0 0
Total fee income 0 0 0
Total net change in unrealized appreciation (depreciation) (57) (246) 315
Total net realized gain (loss) 0 0 0
Control investments | Gibraltar Acquisition LLC      
Schedule Of Investments [Line Items]      
Investments, at fair value: 62,512    
Interest income 3,344    
Total fee income 95    
Total net change in unrealized appreciation (depreciation) 9,656    
Total net realized gain (loss) 0    
Control investments | Gibraltar Business Capital, LLC      
Schedule Of Investments [Line Items]      
Investments, at fair value:   36,944 43,830
Interest income   3,385 3,178
Total fee income   68 54
Total net change in unrealized appreciation (depreciation)   (6,968) (14,616)
Total net realized gain (loss)   0 0
Control investments | Hercules Adviser LLC      
Schedule Of Investments [Line Items]      
Investments, at fair value: 40,713 31,153 20,840
Interest income 608 546 141
Total fee income 0 0 0
Total net change in unrealized appreciation (depreciation) 9,560 7,163 11,955
Total net realized gain (loss) 0 0 0
Control investments | Tectura Corporation      
Schedule Of Investments [Line Items]      
Investments, at fair value: 11,517 8,042 8,269
Interest income 690 690 690
Total fee income 0 0 5
Total net change in unrealized appreciation (depreciation) 3,475 (227) (331)
Total net realized gain (loss) 0 0 0
Affiliate investments      
Schedule Of Investments [Line Items]      
Investments, at fair value:   0 9,458
Total net change in unrealized appreciation (depreciation) 0 4,089 63,806
Total net realized gain (loss) $ 0 1,758 (62,143)
Investment, Affiliated Issuer      
Schedule Of Investments [Line Items]      
Investments, at fair value:   0 9,458
Interest income   1,204 10
Total fee income   0 0
Total net change in unrealized appreciation (depreciation)   4,089 63,806
Total net realized gain (loss)   1,758 (62,143)
Investment, Affiliated Issuer | Black Crow AI, Inc.      
Schedule Of Investments [Line Items]      
Investments, at fair value:   0 1,120
Interest income   0 0
Total fee income   0 0
Total net change in unrealized appreciation (depreciation)   (120) 1,905
Total net realized gain (loss)   3,772 0
Investment, Affiliated Issuer | Pineapple Energy LLC      
Schedule Of Investments [Line Items]      
Investments, at fair value:   0 8,338
Interest income   1,204 10
Total fee income   0 0
Total net change in unrealized appreciation (depreciation)   4,209 (282)
Total net realized gain (loss)   (2,014) 0
Investment, Affiliated Issuer | Solar Spectrum Holdings LLC (p.k.a. Sungevity, Inc.)      
Schedule Of Investments [Line Items]      
Investments, at fair value:     0
Interest income     0
Total fee income     0
Total net change in unrealized appreciation (depreciation)     62,183
Total net realized gain (loss)     (62,143)
Control And Affiliate Issuer Investments Member      
Schedule Of Investments [Line Items]      
Investments, at fair value:   76,458 82,962
Interest income   5,825 4,019
Total fee income   68 59
Total net change in unrealized appreciation (depreciation)   3,811 61,129
Total net realized gain (loss)   $ 1,758 $ (62,143)