GOODWILL AND OTHER INTANGIBLE ASSETS - Goodwill Rollforward (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2020 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 710,071
Foreign currency translation impact	2,604
Other	1,205
Goodwill, ending balance	713,880
Electronic Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	352,797
Foreign currency translation impact	3,448
Other	0
Goodwill, ending balance	356,245
Performance Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	357,274
Foreign currency translation impact	(844)
Other	1,205
Goodwill, ending balance	$ 357,635