Impairment - Wood Treatment - Goodwill Activity (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2020 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 718,647
Foreign currency translation impact	7,055
Impairment	(4,081)
Goodwill, ending balance	721,621
Electronic Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	360,425
Foreign currency translation impact	5,602
Impairment	0
Goodwill, ending balance	366,027
Performance Materials
Goodwill [Roll Forward]
Goodwill, beginning balance	358,222
Foreign currency translation impact	1,453
Impairment	(4,081)
Goodwill, ending balance	$ 355,594