Marketable Securities - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,028,206	$ 3,679
Gross Unrealized Losses	(7,369)
Gross Unrealized Gains	253
Fair Value	1,021,090	3,679
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	536,322
Gross Unrealized Losses	(2,981)
Gross Unrealized Gains	93
Fair Value	533,434
Bank certificates of deposits
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,341	30
Gross Unrealized Losses	(45)
Fair Value	6,296	30
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	372,922	3,624
Gross Unrealized Losses	(4,009)
Gross Unrealized Gains	159
Fair Value	369,072	3,624
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	112,621
Gross Unrealized Losses	(334)
Gross Unrealized Gains	1
Fair Value	$ 112,288
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		25
Fair Value		$ 25

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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