Goodwill and Other Intangible Assets - Goodwill Activity (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 718,647,000	$ 710,071,000
Foreign currency translation impact	3,421,000	7,371,000
Other		1,205,000
Additions due to acquisition	81,960,000
Impairment	(227,126,000)
Goodwill, ending balance	576,902,000	718,647,000	$ 710,071,000
Accumulated impairment amounts		0	0
Electronic Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	360,425,000	352,797,000
Foreign currency translation impact	1,848,000	7,628,000
Other		0
Additions due to acquisition	81,960,000
Impairment	0
Goodwill, ending balance	444,233,000	360,425,000	352,797,000
Performance Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	358,222,000	357,274,000
Foreign currency translation impact	1,573,000	(257,000)
Other		1,205,000
Additions due to acquisition	0
Impairment	(227,126,000)
Goodwill, ending balance	$ 132,669,000	$ 358,222,000	$ 357,274,000