Gladstone Capital Corporation Annual report pursuant to Section 13 and 15(d)

REGISTRATION STATEMENT AND COMMON EQUITY OFFERINGS (Details)		12 Months Ended
	Apr. 04, 2024	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Aug. 31, 2024 USD ($)	Aug. 31, 2022 USD ($)
Government Assistance [Line Items]
Reverse stock split, conversion ratio	0.5
Sale of stock, aggregate value of securities authorized		$ 700,000,000.0
Sale of stock, remaining capacity of aggregate value of securities authorized		$ 689,000,000.0
Common Stock At-the-Market Offerings
Government Assistance [Line Items]
Sale of stock, aggregate offering price authorized				$ 150,000,000	$ 100,000,000.0
Sale of stock, number of shares issued in transaction (in shares) \| shares		476,138	8,774,101
Sale of stock, price (in USD per share) \| $ / shares		$ 23.10	$ 9.96
Sale of stock, gross proceeds from transaction		$ 11,000,000.0	$ 87,400,000
Sale of stock, consideration received on transaction		10,800,000	$ 85,900,000
Sale of stock, remaining capacity of authorized offering price		$ 139,000,000