Restructuring Expenses - Additional Information (Details)	12 Months Ended
	Sep. 30, 2020 USD ($) position	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment charges	$ 45,029,000	$ 0	$ 0
Impairment loss on operating lease assets	28,016,000
Property, Plant and Equipment Impairment or Disposal Disclosure	$ 5,200,000
Number of positions reduced | position	209
Restructuring charges	$ 11,768,000	0	$ 0
Facilities charges
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	$ 0
Employee separation
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 11,768,000