Gladstone Investment Corporation Annual report [Section 13 and 15(d), not S-K Item 405]

REGISTRATION STATEMENT AND COMMON EQUITY OFFERINGS (Details)

REGISTRATION STATEMENT AND COMMON EQUITY OFFERINGS (Details) - USD ($)	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024	May 31, 2024	Apr. 18, 2024	Aug. 31, 2022
Registration Statement on Form N-2 (File No. 333-277452)
Government Assistance [Line Items]
Securities, aggregate value authorized					$ 450,000,000.0
Securities, remaining capacity of aggregate value authorized	$ 119,300,000
Common Stock ATM Program 2024
Government Assistance [Line Items]
Sale of stock, aggregate offering price authorized				$ 75,000,000.0
Remaining capacity of authorized offering price	$ 30,800,000
Sale of stock, number of shares sold (in shares)	2,984,586	148,714
Sale of stock, weighted-average gross price per share (in USD per share)	$ 14.12	$ 13.64
Sale of stock, weighted-average net price per share after deducting commissions and offering costs (in USD per share)	$ 13.92	$ 13.48
Consideration received on transaction	$ 42,100,000	$ 2,000,000.0
Proceeds from issuance of common stock, net of discounts, commissions and offering costs	$ 41,500,000	$ 2,000,000.0
Common Stock ATM Program 2022
Government Assistance [Line Items]
Sale of stock, aggregate offering price authorized						$ 50,000,000.0
Sale of stock, number of shares sold (in shares)		0	3,097,162
Sale of stock, weighted-average gross price per share (in USD per share)			$ 14.37
Sale of stock, weighted-average net price per share after deducting commissions and offering costs (in USD per share)			$ 14.12
Consideration received on transaction			$ 44,500,000
Proceeds from issuance of common stock, net of discounts, commissions and offering costs			$ 43,700,000