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Revenue Recognition - Narrative (Details) - USD ($)
3 Months Ended 6 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Mar. 31, 2021
Mar. 31, 2020
Sep. 30, 2020
Disaggregation of Revenue [Line Items]          
Revenue recognized included in contract liability balance at the beginning of the period     $ 7,900,000 $ 4,800,000  
Impairment losses recognized on contract costs     0 0  
Selling and marketing          
Disaggregation of Revenue [Line Items]          
Contract costs included in selling and marketing expenses $ 300,000 $ 200,000 500,000 $ 400,000  
Other Current and Non-current Assets          
Disaggregation of Revenue [Line Items]          
Contract costs $ 2,200,000   $ 2,200,000   $ 1,500,000