Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 267,583	$ 295,210
Gross Unrealized Gains	0	96
Gross Unrealized Losses	(3,235)	(94)
Fair Value	264,348	295,212
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	85,969	124,678
Gross Unrealized Gains	0	93
Gross Unrealized Losses	(2,022)	(68)
Fair Value	83,947	124,703
U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	98,389	83,061
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(1,213)	(26)
Fair Value	97,176	83,038
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	83,225	87,471
Gross Unrealized Gains	0
Fair Value	$ 83,225	$ 87,471

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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