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Investments - Summary of Investments by Type of Security (Details) - USD ($) $ in Thousands | Sep. 30, 2022 | Sep. 30, 2021
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Cost | $ 70,314 | $ 197,165
Gross Unrealized Gains | 0 | 12
Gross Unrealized Losses | (1,413) | (69)
Fair Market Value | 68,901 | 197,108
Short-term | U.S. Treasury |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 6,016 | 4,222
Gross Unrealized Gains | 0 | 1
Gross Unrealized Losses | (134) | 0
Fair Market Value | 5,882 | 4,223
Short-term | Asset-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost |  | 4,812
Gross Unrealized Gains |  | 1
Gross Unrealized Losses |  | (2)
Fair Market Value |  | 4,811
Short-term | Foreign government and agency securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 2,865 |
Gross Unrealized Gains | 0 |
Gross Unrealized Losses | (38) |
Fair Market Value | 2,827 |
Short-term | Commercial paper |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 18,245 |
Gross Unrealized Gains | 0 |
Gross Unrealized Losses | (223) |
Fair Market Value | 18,022 |
Short-term | Corporate debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 32,065 | 140,042
Gross Unrealized Gains | 0 | 6
Gross Unrealized Losses | (528) | (25)
Fair Market Value | 31,537 | 140,023
Long-term | U.S. Treasury |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 3,431 | 6,996
Gross Unrealized Gains | 0 | 1
Gross Unrealized Losses | (210) | (2)
Fair Market Value | 3,221 | 6,995
Long-term | Foreign government and agency securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 0 | 2,909
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | (1)
Fair Market Value | 0 | 2,908
Long-term | Corporate debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Cost | 7,692 | 38,184
Gross Unrealized Gains | 0 | 3
Gross Unrealized Losses | (280) | (39)
Fair Market Value | $ 7,412 | $ 38,148

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
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