Segment Reporting - Revenue from External Customers (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]
Revenue	$ 324,127	$ 290,528	$ 641,173	$ 578,391
Electronic Materials | Operating segment
Segment Reporting Information [Line Items]
Revenue	274,511	242,547	542,162	479,345
Electronic Materials | CMP slurries | Operating segment
Segment Reporting Information [Line Items]
Revenue	146,540	140,194	292,681	274,915
Electronic Materials | Electronic chemicals | Operating segment
Segment Reporting Information [Line Items]
Revenue	95,111	80,098	186,250	160,104
Electronic Materials | CMP pads | Operating segment
Segment Reporting Information [Line Items]
Revenue	26,815	22,255	50,854	44,326
Electronic Materials | Materials technologies | Operating segment
Segment Reporting Information [Line Items]
Revenue	6,045	0	12,377	0
Performance Materials | Operating segment
Segment Reporting Information [Line Items]
Revenue	49,616	47,981	99,011	99,046
Performance Materials | PIM | Operating segment
Segment Reporting Information [Line Items]
Revenue	30,394	25,987	57,029	51,894
Performance Materials | Wood treatment | Operating segment
Segment Reporting Information [Line Items]
Revenue	10,907	15,546	25,865	32,869
Performance Materials | QED | Operating segment
Segment Reporting Information [Line Items]
Revenue	$ 8,315	$ 6,448	$ 16,117	$ 14,283