Related-Party Transactions - Schedule of Management Fees, Incentive Fees and Associated Credits and Administration Fees (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Adviser
Related Party Transaction [Line Items]
Total fees to Gladstone Securities	$ 2,076	$ 2,148	$ 4,233	$ 4,296
Base management fee | Adviser
Related Party Transaction [Line Items]
Total fees to Gladstone Securities	2,076	2,148	4,233	4,296
Administration Fee
Related Party Transaction [Line Items]
Total fees to Gladstone Securities	553	514	1,156	1,090
Financing Fees and Selling Commissions and Dealer Management Fees | Gladstone Securities
Related Party Transaction [Line Items]
Total fees to Gladstone Securities	2	183	30	332
Selling Commissions and Dealer Management Fees | Gladstone Securities
Related Party Transaction [Line Items]
Total fees to Gladstone Securities	$ 2	$ 183	$ 30	$ 332