Segment Reporting - Reconciliation from Segment Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Net income (loss)	$ 34,571	$ (149,808)	$ 61,999	$ (118,278)
Interest expense, net	9,537	9,495	19,280	19,080
Provision for (benefit from) income taxes	10,979	(16,109)	14,196	(8,563)
Depreciation and amortization	32,762	32,289	65,464	64,180
EBITDA	87,849	(124,133)	160,939	(43,581)
Entegris Transaction-related expenses	12,243	0	18,293	0
Impairment charges	0	208,221	9,435	215,568
Net costs related to restructuring	219	46	245	72
Costs related to the Pandemic, net of grants received	0	(421)	0	841
Acquisition and integration-related expenses	(540)	2,167	(233)	4,536
Costs related to KMG-Bernuth warehouse fire, net of recoveries	(3,500)	(1,076)	(3,500)	(1,076)
Consolidated adjusted EBITDA	96,316	84,804	188,203	176,360
Operating segment | Electronic Materials
Segment Reporting Information [Line Items]
Consolidated adjusted EBITDA	93,957	81,315	182,039	162,071
Operating segment | Performance Materials
Segment Reporting Information [Line Items]
Consolidated adjusted EBITDA	13,901	18,750	28,902	41,725
Corporate
Segment Reporting Information [Line Items]
Unallocated corporate expenses	(11,542)	(15,261)	(22,738)	(27,436)
Future Forward Program
Segment Reporting Information [Line Items]
Net costs related to restructuring	$ 45	$ 0	$ 3,024	$ 0