INTANGIBLE ASSETS - Intangible Assets, net by major class (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Finite-Lived intangible assets
Carrying Amount, Gross	$ 378,749	$ 377,994
Accumulated Amortization	(78,400)	(69,566)
Carrying Amount, Net	300,350	308,428
Client relationships
Finite-Lived intangible assets
Carrying Amount, Gross	317,492	316,820
Accumulated Amortization	(61,771)	(54,711)
Carrying Amount, Net	255,722	262,109
Intellectual property
Finite-Lived intangible assets
Carrying Amount, Gross	56,420	56,337
Accumulated Amortization	(13,868)	(12,234)
Carrying Amount, Net	42,552	44,103
Other
Finite-Lived intangible assets
Carrying Amount, Gross	4,837	4,837
Accumulated Amortization	(2,761)	(2,621)
Carrying Amount, Net	$ 2,076	$ 2,216