Marketable Securities - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Sep. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 840,116	$ 1,278,422
Gross Unrealized Losses	(12,562)	(14,660)
Gross Unrealized Gains	18	22
Fair Value	827,572	1,263,784
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	479,617	804,774
Gross Unrealized Losses	(5,434)	(6,163)
Gross Unrealized Gains	13	21
Fair Value	474,196	798,632
Bank certificates of deposits
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,549	8,335
Gross Unrealized Losses	(174)	(158)
Gross Unrealized Gains	5	1
Fair Value	10,380	8,178
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	341,317	406,270
Gross Unrealized Losses	(6,941)	(8,113)
Fair Value	334,376	398,157
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,633	59,043
Gross Unrealized Losses	(13)	(226)
Fair Value	$ 8,620	$ 58,817

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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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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