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Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	$ 80,575	$ 21,547
Cost or amortized cost	296,396	483,931
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1	145
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(2,252)	(121)
Fair value	294,145	483,955
Debt Securities, Available-for-sale, Current	196,458	329,630
Debt Securities, Available-for-sale, Noncurrent	17,112	132,778
Equity Securities, FV-NI	2,000
Equity Securities, FV-NI, Current	0
Equity Securities, FV-NI, Noncurrent	2,000
Available-for-sale Securities	296,145
Available-for-sale Securities, Current	196,458	329,630
Long-term investments	19,112	132,778
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	79,183	17,150
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cost or amortized cost	250	255
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
Corporate Bonds and Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cost or amortized cost	93,016	243,568
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1	129
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(1,086)	(86)
Municipal Bonds and Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cost or amortized cost	7,661	24,684
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(110)	(9)
U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cost or amortized cost	110,639	162,221
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	14
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(979)	(12)
U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cost or amortized cost	5,647	36,053
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(77)	(14)
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Equity Securities, FV-NI	2,000
Equity Securities, FV-NI, Current	0
Equity Securities, FV-NI, Noncurrent	2,000
Fair Value, Recurring | Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	79,183	17,150
Fair Value, Recurring | Level 2 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair value	250	255
Debt Securities, Available-for-sale, Current	250	255
Debt Securities, Available-for-sale, Noncurrent	0	0
Fair Value, Recurring | Level 2 | Corporate Bonds and Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value		4,397
Fair value	91,931	243,611
Debt Securities, Available-for-sale, Current	81,499	186,107
Debt Securities, Available-for-sale, Noncurrent	10,432	53,107
Fair Value, Recurring | Level 2 | Municipal Bonds and Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	1,392
Fair value	7,551	24,677
Debt Securities, Available-for-sale, Current	4,013	13,566
Debt Securities, Available-for-sale, Noncurrent	2,146	11,111
Fair Value, Recurring | Level 2 | U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair value	109,660	162,223
Debt Securities, Available-for-sale, Current	106,855	102,615
Debt Securities, Available-for-sale, Noncurrent	2,805	59,608
Fair Value, Recurring | Level 2 | U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair value	5,570	36,039
Debt Securities, Available-for-sale, Current	3,841	27,087
Debt Securities, Available-for-sale, Noncurrent	$ 1,729	$ 8,952

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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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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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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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