Supplementary Balance Sheet Information - Summary of Account Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Valuation and Qualifying Accounts Disclosure [Line Items]
Accounts receivable	$ 195,587	$ 169,317
Less allowance for doubtful accounts	(7,216)	(3,644)
Accounts receivable, net	188,291	165,602
Allowance for Sales Returns
Valuation and Qualifying Accounts Disclosure [Line Items]
Less allowance for sales returns	$ (80)	$ (71)	$ (45)	$ (81)