Investments - Current Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Current investments, Adjusted Basis	$ 689,882	$ 577,465
Current investments, Gross Unrealized Gains	2,956	837
Current investments, Gross Unrealized Losses	(20)	(26)
Current investments, Fair Value	692,818	578,276
Available-for-sale securities
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Current investments, Adjusted Basis	689,882	577,465
Current investments, Gross Unrealized Gains	2,956	837
Current investments, Gross Unrealized Losses	(20)	(26)
Current investments, Fair Value	$ 692,818	$ 578,276

Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, Current

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- Definition

Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, Current

+ References

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- Definition

Schedule of held to maturity securities and marketable securities.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481830/320-10-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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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), classified as current.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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