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Investments - Summary of Investments by Type of Security (Details) - USD ($)
$ in Thousands
Dec. 31, 2021
Sep. 30, 2021
Schedule Of Available For Sale Securities [Line Items]    
Cost $ 194,333 $ 197,165
Gross Unrealized Gains 1 12
Gross Unrealized Losses (326) (69)
Fair Market Value 194,008 197,108
Short-term investments | U.S. Treasury    
Schedule Of Available For Sale Securities [Line Items]    
Cost 7,711 4,222
Gross Unrealized Gains 0 1
Gross Unrealized Losses (11) 0
Fair Market Value 7,700 4,223
Short-term investments | Asset-backed securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost 4,514 4,812
Gross Unrealized Gains 0 1
Gross Unrealized Losses (2) (2)
Fair Market Value 4,512 4,811
Short-term investments | Corporate debt securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost 125,632 140,042
Gross Unrealized Gains 1 6
Gross Unrealized Losses (92) (25)
Fair Market Value 125,541 140,023
Long-term investments | U.S. Treasury    
Schedule Of Available For Sale Securities [Line Items]    
Cost 7,497 6,996
Gross Unrealized Gains 0 1
Gross Unrealized Losses (29) (2)
Fair Market Value 7,468 6,995
Long-term investments | Corporate debt securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost 46,081 38,184
Gross Unrealized Gains 0 3
Gross Unrealized Losses (181) (39)
Fair Market Value 45,900 38,148
Long-term investments | Foreign government and agency securities    
Schedule Of Available For Sale Securities [Line Items]    
Cost 2,898 2,909
Gross Unrealized Gains 0 0
Gross Unrealized Losses (11) (1)
Fair Market Value $ 2,887 $ 2,908