CONSOLIDATED STATEMENTS OF CHANGES IN NET ASSETS (Parentheticals) - $ / shares	3 Months Ended	6 Months Ended
Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2023	Mar. 31, 2022
Statement of Stockholders' Equity [Abstract]
Net investment income (in USD per share)	$ 0.23	$ 0.21	$ 0.20	$ 0.20	$ 0.44	$ 0.40

Investment Company, Distribution to Shareholders from Net Investment Income, Per Share

No definition available.

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Namespace Prefix:	glad_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration