Debt - Summary of Commitments, Borrowings Outstanding and Fair Value of Notes (Details) - Unsecured Notes - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Commitments	$ 143,110	$ 145,933
Total Amount Outstanding	143,110	145,933
Fair Value	139,912	142,277
GECCM Notes
Debt Instrument [Line Items]
Commitments	45,610	45,610
Total Amount Outstanding	45,610	45,610
Fair Value	45,410	45,081
GECCN Notes
Debt Instrument [Line Items]
Commitments		42,823
Total Amount Outstanding		42,823
Fair Value		42,686
GECCO Notes
Debt Instrument [Line Items]
Commitments	57,500	57,500
Total Amount Outstanding	57,500	57,500
Fair Value	55,062	$ 54,510
GECCZ Notes
Debt Instrument [Line Items]
Commitments	40,000
Total Amount Outstanding	40,000
Fair Value	$ 39,440