Summary of Significant Accounting Policies and Select Balance Sheet Information - Amortized Cost, Unrealized Holding Gains and (Losses) and Fair Value of Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 9,718	$ 30,313
Unrealized Gains	2	19
Unrealized Losses	(1)	(19)
Fair Value	9,719	30,313
Current Assets	7,717	30,313
Noncurrent Assets	2,002
Commercial paper and corporate bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,718	30,313
Unrealized Gains	2	19
Unrealized Losses	(1)	(19)
Fair Value	9,719	30,313
Current Assets	7,717	$ 30,313
Noncurrent Assets	$ 2,002