Gladstone Capital Corporation Quarterly report [Sections 13 or 15(d)]

Quarterly report [Sections 13 or 15(d)]

BORROWINGS - Notes Payable Narrative (Details)

BORROWINGS - Notes Payable Narrative (Details) $ / shares in Units, $ in Thousands			1 Months Ended							9 Months Ended
	Oct. 15, 2025 USD ($)	Sep. 22, 2025 $ / shares	Jun. 30, 2026 USD ($)	Oct. 31, 2025 USD ($)	Sep. 30, 2025 USD ($) day $ / shares	Aug. 31, 2023 USD ($)	Nov. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Apr. 30, 2022
Debt Instrument [Line Items]
Aggregate amount			$ 259,500							$ 259,500	$ 257,000
Proceeds from issuance of long term debt										60,000	$ 0
Interest payable			3,523		$ 3,141					3,523
Convertible Debt \| 2030 Convertible Notes
Debt Instrument [Line Items]
Aggregate principal amount					$ 149,500
Interest rate					5.875%
Proceeds from convertible debt					$ 142,800
Interest payable					$ 8,800
Conversion rate		0.03861			0.0384394
Conversion price (in dollars per share) \| $ / shares		$ 25.90			$ 26.02
Threshold percentage of stock price trigger					130.00%
Threshold trading days \| day					20
Threshold consecutive trading days \| day					30
Redemption price					100.00%
Convertible debt, fair value			143,700							143,700
Convertible Debt \| 2030 Convertible Notes \| Maximum
Debt Instrument [Line Items]
Conversion rate					0.0422834
Notes Payable \| 7.0% Notes due 2029
Debt Instrument [Line Items]
Aggregate principal amount			$ 60,000							$ 60,000
Interest rate			7.00%							7.00%
Proceeds from issuance of long term debt			$ 58,800
Note payable, fair value			$ 60,000							$ 60,000
Notes Payable \| 7.75% Notes due 2028
Debt Instrument [Line Items]
Interest rate			7.00%			7.75%				7.00%
Interest due annually			$ 4,200							$ 4,200
Aggregate amount						$ 57,000
Proceeds from issuance of long term debt						$ 55,100
Repurchased face amount	$ 57,000
Loss on extinguishment of debt	$ 1,200
Notes Payable \| 3.75% Notes due 2027
Debt Instrument [Line Items]
Interest rate							3.75%					3.75%
Aggregate amount							$ 50,000
Proceeds from issuance of long term debt							48,500
Interest payable							$ 1,900
Note payable, fair value			$ 48,700							$ 48,700
Notes Payable \| 5.125% Notes due 2026
Debt Instrument [Line Items]
Interest rate									5.125%
Aggregate amount								$ 50,000	$ 100,000
Proceeds from issuance of long term debt								$ 50,600	$ 97,700
Repurchased face amount				$ 150,000
Loss on extinguishment of debt				$ 200