Marketable Securities - Summary of Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 346,657	$ 457,081
Gross Unrealized Losses	(3,483)	(6,870)
Fair Value	343,174	450,211
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	148,119	227,804
Gross Unrealized Losses	(1,200)	(2,573)
Fair Value	146,919	225,231
Bank certificates of deposits
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,842	8,122
Gross Unrealized Losses	(94)	(170)
Fair Value	7,748	7,952
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	190,696	221,155
Gross Unrealized Losses	(2,189)	(4,127)
Fair Value	$ 188,507	$ 217,028