Fair Value Measurement - Summary of Reconciliation of Beginning and Ending Balances of the Level 3 Instruments (Detail) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, beginning balance		$ 631	$ 644
Change in fair value recorded in other income (expense), net		(631)	(13)
Fair value, ending balance			631
Series A Redeemable Convertible Preferred Stock [Member]
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, beginning balance		365	331
Change in fair value recorded in other income (expense), net		(365)	34
Fair value, ending balance			365
Series B Redeemable Convertible Preferred Stock [Member]
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, beginning balance		94	110
Change in fair value recorded in other income (expense), net		(94)	(16)
Fair value, ending balance			94
Series C Redeemable Convertible Preferred Stock [Member]
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, beginning balance		130	152
Change in fair value recorded in other income (expense), net		(130)	(22)
Fair value, ending balance			130
Series D Redeemable Convertible Preferred Stock [Member]
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, beginning balance		42	51
Change in fair value recorded in other income (expense), net		(42)	(9)
Fair value, ending balance			$ 42