Balance sheet components - Schedule Of Property Plant And Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 54,944	$ 43,828
Less: Accumulated depreciation and amortization	(29,478)	(22,993)
Property, Plant and Equipment, Net	25,466	20,835
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	37,338	26,021
Furniture, fixtures and other equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,728	1,760
Computer equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,834	2,777
Computer software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,678	3,507
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,669	3,772
Construction in progress
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 4,697	$ 5,991