Postretirement Benefits - Fair Value of Plan Assets (Details) $ in Thousands	Sep. 30, 2020 USD ($) plan	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, number of plans | plan	3
Fair value of plan assets | $	$ 7,500	$ 6,574	$ 7,078
SWITZERLAND
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, number of plans | plan	2
Fair value of plan assets | $	$ 7,371	6,486
TAIWAN, PROVINCE OF CHINA
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, number of plans | plan	1
Fair value of plan assets | $	$ 129	$ 88