Gladstone Capital Corporation Quarterly report pursuant to Section 13 or 15(d)

Quarterly report pursuant to Section 13 or 15(d)

BORROWINGS - Revolving Line of Credit Narrative (Details)

BORROWINGS - Revolving Line of Credit Narrative (Details) - Credit Facility - Line of Credit	9 Months Ended
	Jun. 30, 2024 USD ($) obligor	Jun. 27, 2024 USD ($)	Jun. 26, 2024 USD ($)	Mar. 28, 2024 USD ($)	Mar. 27, 2024 USD ($)	Dec. 12, 2023 USD ($)	Dec. 11, 2023 USD ($)	Sep. 30, 2023 USD ($)
Revolving Line of Credit
Debt Instrument [Line Items]
Commitment amount	$ 268,659,000							$ 223,659,000
Line of credit facility, accordion feature maximum borrowing capacity	$ 350,000,000
Debt instrument, covenant, borrowing base, minimum number of obligors \| obligor	25
Covenant, required minimum net worth of mandatory redeemable term preferred stock	$ 325,000,000.0
Covenant, required minimum net worth of mandatory redeemable term preferred stock, plus percent of all equity and subordinated debt raised	50.00%
Covenant, required minimum net worth of mandatory redeemable term preferred stock, minus percent of any equity or subordinated debt redeemed or retired	50.00%
Covenant, required minimum net worth of mandatory redeemable term preferred stock, plus percent of all equity and subordinated debt raised, minus percent of any equity or subordinated debt redeemed or retired	$ 412,000,000.0
Debt instrument, covenant, senior security, indebtedness, required minimum asset coverage ratio	150.00%
Senior security, indebtedness, asset coverage amount	$ 691,800,000
Indebtedness asset coverage on our senior securities	234.60%
Investment company, number of obligor \| obligor	34
Revolving Line of Credit \| SOFR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.10%
Revolving Line of Credit \| Secured Overnight Financing Rate (SOFR), Tranche One
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.00%
Revolving Line of Credit \| Secured Overnight Financing Rate (SOFR), Thereafter
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.50%
Revolving Line of Credit - Amendment No. 5
Debt Instrument [Line Items]
Commitment amount						$ 233,700,000	$ 223,700,000
Revolving Line of Credit - Amendment No. 6
Debt Instrument [Line Items]
Commitment amount				$ 243,700,000	$ 233,700,000
Revolving Line of Credit - Amendment No. 7
Debt Instrument [Line Items]
Commitment amount		$ 268,700,000	$ 243,700,000