Postretirement Benefits - Fair Value of Plan Assets (Details) $ in Thousands	Sep. 30, 2018 USD ($) plan	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, number of plans | plan	3
Fair value of plan assets | $	$ 7,078	$ 2,225	$ 4,532
SWITZERLAND
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, number of plans | plan	2
Fair value of plan assets | $	$ 6,754	1,886
TAIWAN, PROVINCE OF CHINA
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, number of plans | plan	1
Fair value of plan assets | $	$ 324	$ 339