Income Taxes - Summary of Income (Loss) Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Domestic	$ (73,865)	$ (112,077)	$ (114,591)
Foreign	208,571	132,377	143,247
Income before income taxes	$ 134,706	$ 20,300	$ 28,656