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Investments - Summary of Investments by Type of Security (Details) - USD ($) $ in Thousands | Jun. 30, 2020 | Sep. 30, 2019
--- | --- | ---
Schedule Of Available For Sale Securities [Line Items] |  |
Cost | $ 33,061 | $ 18,051
Gross Unrealized Gains | 162 | 4
Gross Unrealized Losses | 0 | (1)
Fair Market Value | 33,223 | 18,054
Short-term investments | U.S. Treasury |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Cost | 8,245 | 4,240
Gross Unrealized Gains | 62 | 2
Gross Unrealized Losses | 0 | 0
Fair Market Value | 8,307 | 4,242
Short-term investments | Asset-backed securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Cost | 3,769 |
Gross Unrealized Gains | 34 |
Gross Unrealized Losses | 0 |
Fair Market Value | 3,803 |
Short-term investments | Corporate debt securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Cost | 18,147 | 12,258
Gross Unrealized Gains | 24 | 2
Gross Unrealized Losses | 0 | 0
Fair Market Value | 18,171 | 12,260
Long-term investments | U.S. Treasury |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Cost |  | 1,102
Gross Unrealized Gains |  | 0
Gross Unrealized Losses |  | (1)
Fair Market Value |  | 1,101
Long-term investments | Asset-backed securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Cost | 964 |
Gross Unrealized Gains | 14 |
Gross Unrealized Losses | 0 |
Fair Market Value | 978 |
Long-term investments | Corporate debt securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Cost | 1,936 | 451
Gross Unrealized Gains | 28 | 0
Gross Unrealized Losses | 0 | 0
Fair Market Value | $ 1,964 | $ 451

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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 http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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