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Fair Value Assets - Measured on a Recurring Basis (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Sep. 30, 2022
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents, fair value | $ 392,592 | $ 287,932
Debt Securities, Available-for-sale, Amortized Cost | 398,852 | 422,699
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax | (100) | (1,787)
Debt Securities, Available-for-Sale | 398,752 | 420,912
Debt Securities, Available-for-sale, Current | 6,160 | 126,554
Debt Securities, Available-for-sale, Noncurrent | 0 | 6,426
Equity Securities, FV-NI | 5,068 | 3,118
Equity Securities, FV-NI, Current | 0 | 0
Equity Securities, FV-NI, Noncurrent | 5,068 | 3,118
Investments, Fair Value Disclosure | 403,820 | 424,030
Short-term investments | 6,160 | 126,554
Long-term investments | 5,068 | 9,544
Money Market Funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents, fair value | 392,592 | 276,294
Corporate Bonds And Notes [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 4,412 | 50,828
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax | (88) | (950)
Municipal Bonds And Notes [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 1,108 | 5,018
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax | (9) | (102)
US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 0 | 84,734
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax | 0 | (660)
US Government Agencies Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 740 | 5,825
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax | 0 | 0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax | (3) | (75)
Fair Value, Recurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Equity Securities, FV-NI | 5,068 | 3,118
Equity Securities, FV-NI, Current | 0 | 0
Equity Securities, FV-NI, Noncurrent | 5,068 | 3,118
Fair Value, Recurring [Member] | Level 1 | Money Market Funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents, fair value | 392,592 | 276,294
Fair Value, Recurring [Member] | Level 2 | Corporate Bonds And Notes [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents, fair value |  | 912
Debt Securities, Available-for-Sale | 4,324 | 49,878
Debt Securities, Available-for-sale, Current | 4,324 | 44,356
Debt Securities, Available-for-sale, Noncurrent | 0 | 4,610
Fair Value, Recurring [Member] | Level 2 | Municipal Bonds And Notes [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Debt Securities, Available-for-Sale | 1,099 | 4,916
Debt Securities, Available-for-sale, Current | 1,099 | 3,812
Debt Securities, Available-for-sale, Noncurrent | 0 | 1,104
Fair Value, Recurring [Member] | Level 2 | US Government Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents, fair value |  | 10,120
Debt Securities, Available-for-Sale | 0 | 84,074
Debt Securities, Available-for-sale, Current | 0 | 73,954
Debt Securities, Available-for-sale, Noncurrent | 0 | 0
Fair Value, Recurring [Member] | Level 2 | US Government Agencies Debt Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents, fair value |  | 606
Debt Securities, Available-for-Sale | 737 | 5,750
Debt Securities, Available-for-sale, Current | 737 | 4,432
Debt Securities, Available-for-sale, Noncurrent | $ 0 | $ 712

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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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