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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

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