DISTRIBUTIONS TO COMMON STOCKHOLDERS - Adjustments for Book-tax Differences to Reflect Tax Character (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2023	Sep. 30, 2022
Undistributed net investment income
Investment Company, Changes in Net Assets [Line Items]
Tax reclassification, increase (decrease)	$ 71	$ (5,606)
Accumulated net realized losses
Investment Company, Changes in Net Assets [Line Items]
Tax reclassification, increase (decrease)	(71)	7,013
Capital in excess of par value
Investment Company, Changes in Net Assets [Line Items]
Tax reclassification, increase (decrease)	$ 0	$ (1,407)