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Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands | Dec. 31, 2021 | Sep. 30, 2021
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Cash equivalents, fair value | $ 20,044 | $ 21,547
Investments, fair value | 443,583 | 483,955
Certificates of Deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 992 | 255
Corporate Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 177,093 | 186,107
Debt Securities, Available-for-sale, Noncurrent | 48,638 | 53,107
Municipal Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 15,359 | 13,566
Debt Securities, Available-for-sale, Noncurrent | 2,239 | 11,111
U.S. Government Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 135,934 | 102,615
Debt Securities, Available-for-sale, Noncurrent | 24,341 | 59,608
U.S. Government Agency Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 17,170 | 27,087
Debt Securities, Available-for-sale, Noncurrent | 1,773 | 8,952
Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Cash equivalents, fair value | 19,265 | 17,150
Investments, fair value | 19,265 | 17,150
Level 1 | Certificates of Deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Level 1 | Corporate Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Level 1 | Municipal Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Level 1 | U.S. Government Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Level 1 | U.S. Government Agency Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Cash equivalents, fair value | 779 | 4,397
Investments, fair value | 424,318 | 466,805
Level 2 | Certificates of Deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 992 | 255
Level 2 | Corporate Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 177,093 | 186,107
Debt Securities, Available-for-sale, Noncurrent | 48,638 | 53,107
Level 2 | Municipal Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 15,359 | 13,566
Debt Securities, Available-for-sale, Noncurrent | 2,239 | 11,111
Level 2 | U.S. Government Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 135,934 | 102,615
Debt Securities, Available-for-sale, Noncurrent | 24,341 | 59,608
Level 2 | U.S. Government Agency Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 17,170 | 27,087
Debt Securities, Available-for-sale, Noncurrent | 1,773 | 8,952
Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Cash equivalents, fair value | 0 | 0
Investments, fair value | 0 | 0
Level 3 | Certificates of Deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Level 3 | Corporate Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Level 3 | Municipal Bonds and Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Level 3 | U.S. Government Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Level 3 | U.S. Government Agency Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] |  |
Debt Securities, Available-for-sale, Current | 0 | 0
Debt Securities, Available-for-sale, Noncurrent | $ 0 | $ 0

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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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