Fair Value Assets - Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
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

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), classified as current.

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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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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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