SEGMENT AND GEOGRAPHIC INFORMATION - Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023
SEGMENT INFORMATION
Revenue	$ 119,035	$ 151,463	$ 254,536	$ 274,217
Long-lived assets	191,423		191,423		$ 191,068
United States
SEGMENT INFORMATION
Revenue	102,429	129,980	214,198	228,989
Long-lived assets	174,664		174,664		178,021
Netherlands
SEGMENT INFORMATION
Revenue	9,724	11,522	27,786	26,744
Long-lived assets	6,619		6,619		6,656
Other
SEGMENT INFORMATION
Revenue	6,882	$ 9,961	12,552	$ 18,484
Long-lived assets	$ 10,140		$ 10,140		$ 6,391