SEGMENT AND GEOGRAPHIC INFORMATION - Geographic Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
SEGMENT INFORMATION
Revenue	$ 572,425	$ 547,656
Long-lived assets	191,068	186,199
United States
SEGMENT INFORMATION
Revenue	482,630	471,886
Long-lived assets	178,021	173,417
Netherlands
SEGMENT INFORMATION
Revenue	54,088	42,361
Long-lived assets	6,656	5,824
Other
SEGMENT INFORMATION
Revenue	35,707	33,409
Long-lived assets	$ 6,391	$ 6,958