Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Sep. 30, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	$ 624,080	$ 437,273
Cost or amortized cost	624,080	437,273
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	0
Fair value	624,080	437,273
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0	0
Equity Securities, FV-NI	12,534	8,580
Equity Securities, FV-NI, Current	0	0
Equity Securities, FV-NI, Noncurrent	12,534	8,580
Available-for-sale Securities	636,614	445,853
Available-for-sale Securities, Current	0	0
Long-term investments	12,534	8,580
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Equity Securities, FV-NI	12,534	8,580
Equity Securities, FV-NI, Current	0	0
Equity Securities, FV-NI, Noncurrent	12,534	8,580
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	624,080	437,273
Money Market Funds \| Fair Value, Recurring \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	$ 624,080	$ 437,273

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).

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Amount, before tax, of unrealized loss 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).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as noncurrent.

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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.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as noncurrent.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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