Goodwill - Goodwill Rollforward (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2022	Sep. 30, 2021
Goodwill [Line Items]
Accumulated impairment amounts	$ 236,561	$ 227,126
Goodwill [Roll Forward]
Goodwill, beginning balance	576,902
Foreign currency translation impact	(3,188)
Impairment	(9,435)
Goodwill, ending balance	564,279
Electronic Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	444,233
Foreign currency translation impact	(3,393)
Impairment	0
Goodwill, ending balance	440,840
Performance Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	132,669
Foreign currency translation impact	205
Impairment	(9,435)
Goodwill, ending balance	$ 123,439