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Investments - Summary of Investments by Type of Security (Details) - USD ($)
$ in Thousands
Mar. 31, 2022
Sep. 30, 2021
Schedule Of Available For Sale Securities [Line Items]    
Cost $ 70,558 $ 197,165
Gross Unrealized Gains 0 12
Gross Unrealized Losses (1,155) (69)
Short-term investments: 37,910 149,057
Long-term investments: 31,493 48,051
Fair Market Value 69,403 197,108
U.S. Treasury    
Schedule Of Available For Sale Securities [Line Items]    
Amortized cost, short-term 2,000 4,222
Amortized cost, long-term 7,481 6,996
Gross Unrealized Gains, short-term 0 1
Gross Unrealized Gains, long-term 0 1
Gross Unrealized Losses, short-term (20) 0
Gross Unrealized Losses, long-term (215) (2)
Short-term investments: 1,980 4,223
Long-term investments: 7,266 6,995
Foreign government and agency securities    
Schedule Of Available For Sale Securities [Line Items]    
Amortized cost, short-term 2,888  
Amortized cost, long-term   2,909
Gross Unrealized Gains, short-term 0  
Gross Unrealized Gains, long-term   0
Gross Unrealized Losses, short-term (38)  
Gross Unrealized Losses, long-term   (1)
Short-term investments: 2,850  
Long-term investments:   2,908
Asset-backed securities    
Schedule Of Available For Sale Securities [Line Items]    
Amortized cost, short-term   4,812
Gross Unrealized Gains, short-term   1
Gross Unrealized Losses, short-term   (2)
Short-term investments:   4,811
Corporate debt securities    
Schedule Of Available For Sale Securities [Line Items]    
Amortized cost, short-term 33,446 140,042
Amortized cost, long-term 24,743 38,184
Gross Unrealized Gains, short-term 0 6
Gross Unrealized Gains, long-term 0 3
Gross Unrealized Losses, short-term (366) (25)
Gross Unrealized Losses, long-term (516) (39)
Short-term investments: 33,080 140,023
Long-term investments: $ 24,227 $ 38,148