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	6 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) obligor	Sep. 30, 2023 USD ($)	Mar. 28, 2024 USD ($)	Mar. 27, 2024 USD ($)	Dec. 12, 2023 USD ($)	Dec. 11, 2023 USD ($)	Mar. 31, 2023 obligor
Revolving Line of Credit
Debt Instrument [Line Items]
Commitment amount	$ 243,659,000	$ 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
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	$ 409,800,000
Debt instrument, covenant, senior security, indebtedness, required minimum asset coverage ratio	150.00%
Senior security, indebtedness, asset coverage amount	$ 683,300,000
Indebtedness asset coverage on our senior securities	213.40%
Investment company, number of obligor \| obligor	36						36
Revolving Line of Credit \| SOFR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	0.10%	3.10%
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 \| One-Month Term Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.10%
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