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Fair Value Measurements - Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) | Sep. 30, 2022 | Sep. 30, 2021
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable debt securities | $ 0 | $ 126,728,000
Fair Value, Measurements, Recurring |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable debt securities |  | 126,728,000
Fair Value, Measurements, Recurring | Money market instruments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Money market instruments | 39,262,000 | 160,032,000
Fair Value, Measurements, Recurring | U.S. government bonds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 1,973,000 |
Fair Value, Measurements, Recurring | Commercial notes |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 41,727,000 |
Fair Value, Measurements, Recurring | Corporate debt securities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 271,333,000 | 254,073,000
Fair Value, Measurements, Recurring | Certificate of deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 50,000,000 | 50,000,000
Fair Value, Measurements, Recurring | Level 1 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable debt securities |  | 126,728,000
Fair Value, Measurements, Recurring | Level 1 | Money market instruments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Money market instruments | 39,262,000 | 160,032,000
Fair Value, Measurements, Recurring | Level 1 | U.S. government bonds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 1,973,000 |
Fair Value, Measurements, Recurring | Level 1 | Commercial notes |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 0 |
Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Certificate of deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 50,000,000 | 50,000,000
Fair Value, Measurements, Recurring | Level 2 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable debt securities |  | 0
Fair Value, Measurements, Recurring | Level 2 | Money market instruments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Money market instruments | 0 | 0
Fair Value, Measurements, Recurring | Level 2 | U.S. government bonds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 0 |
Fair Value, Measurements, Recurring | Level 2 | Commercial notes |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 41,727,000 |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 271,333,000 | 254,073,000
Fair Value, Measurements, Recurring | Level 2 | Certificate of deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable debt securities |  | 0
Fair Value, Measurements, Recurring | Level 3 | Money market instruments |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Money market instruments | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | U.S. government bonds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 0 |
Fair Value, Measurements, Recurring | Level 3 | Commercial notes |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 0 |
Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Certificate of deposits |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Held to maturity securities | $ 0 | $ 0

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- Definition Amount of 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://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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