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Short-Term and Long-Term Investments - Schedule of Short-Term and Long-Term Investments (Details) - USD ($)
$ in Thousands
 3 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Sep. 30, 2021
Schedule of Investments [Line Items]      
Interest income from investments $ 300 $ 1,100  
Short-Term Investments      
Schedule of Investments [Line Items]      
Cost or amortized cost 346,901   $ 329,571
Gross unrealized gains 10   129
Gross unrealized losses (363)   (70)
Fair value 346,548   329,630
Short-Term Investments | Certificates of Deposit      
Schedule of Investments [Line Items]      
Cost or amortized cost 992   255
Gross unrealized gains 0   0
Gross unrealized losses 0   0
Fair value 992   255
Short-Term Investments | Corporate Bonds and Notes      
Schedule of Investments [Line Items]      
Cost or amortized cost 177,248   186,043
Gross unrealized gains 10   116
Gross unrealized losses (165)   (52)
Fair value 177,093   186,107
Short-Term Investments | Municipal Bonds and Notes      
Schedule of Investments [Line Items]      
Cost or amortized cost 15,377   13,570
Gross unrealized gains 0   1
Gross unrealized losses (18)   (5)
Fair value 15,359   13,566
Short-Term Investments | U.S. Government Securities      
Schedule of Investments [Line Items]      
Cost or amortized cost 136,091   102,607
Gross unrealized gains 0   12
Gross unrealized losses (157)   (4)
Fair value 135,934   102,615
Short-Term Investments | U.S. Government Agency Securities      
Schedule of Investments [Line Items]      
Cost or amortized cost 17,193   27,096
Gross unrealized gains 0   0
Gross unrealized losses (23)   (9)
Fair value 17,170   27,087
Long-Term Investments      
Schedule of Investments [Line Items]      
Cost or amortized cost 77,316   132,813
Gross unrealized gains 0   16
Gross unrealized losses (325)   (51)
Fair value 76,991   132,778
Long-Term Investments | Corporate Bonds and Notes      
Schedule of Investments [Line Items]      
Cost or amortized cost 48,845   53,128
Gross unrealized gains 0   13
Gross unrealized losses (207)   (34)
Fair value 48,638   53,107
Long-Term Investments | Municipal Bonds and Notes      
Schedule of Investments [Line Items]      
Cost or amortized cost 2,262   11,114
Gross unrealized gains 0   1
Gross unrealized losses (23)   (4)
Fair value 2,239   11,111
Long-Term Investments | U.S. Government Securities      
Schedule of Investments [Line Items]      
Cost or amortized cost 24,426   59,614
Gross unrealized gains 0   2
Gross unrealized losses (85)   (8)
Fair value 24,341   59,608
Long-Term Investments | U.S. Government Agency Securities      
Schedule of Investments [Line Items]      
Cost or amortized cost 1,783   8,957
Gross unrealized gains 0   0
Gross unrealized losses (10)   (5)
Fair value $ 1,773   $ 8,952