Annual report pursuant to Section 13 and 15(d)

Income taxes - Narrative (Details)

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Income taxes - Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Net operating loss carryforwards      
Cash and cash equivalents $ 135,061 $ 71,737  
Unrecognized tax benefits that, if recognized, would affect the annual effective income tax rate 12,600 1,800  
Interest and penalties included in net liability balance 2,100 100  
Maximum      
Net operating loss carryforwards      
Interest expense recognized related to unrecognized tax benefits (less than) 100 $ 100 $ 100
Foreign Tax Authority      
Net operating loss carryforwards      
Cash and cash equivalents $ 84,400