Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Jun. 30, 2023	Sep. 30, 2022
Assets:
Marketable securities		$ 32,047	$ 24,515
Cash deposits		135,200	113,900
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	27,803	19,314
Marketable securities	[2]	32,047	24,515
Total		59,850	43,829
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	27,803	19,314
Marketable securities	[2]	32,047	24,515
Total		$ 59,850	$ 43,829

[1] Included in cash and cash equivalents on our condensed consolidated balance sheets at June 30, 2023 and September 30, 2022. Not included in these tables are cash deposits of $135.2 million and $113.9 million at June 30, 2023 and September 30, 2022, respectively.

[2] Represents securities held under a supplemental retirement and savings plan for certain officers and senior management employees, which are distributed upon termination or retirement of the employees. Included in marketable securities on our condensed consolidated balance sheets at June 30, 2023 and September 30, 2022.