Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Mar. 31, 2023	Sep. 30, 2022
Assets:
Marketable securities		$ 29,580	$ 24,515
Cash deposits		114,300	113,900
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	23,501	19,314
Marketable securities	[2]	29,580	24,515
Total		53,081	43,829
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	23,501	19,314
Marketable securities	[2]	29,580	24,515
Total		$ 53,081	$ 43,829

[1] Included in cash and cash equivalents on our condensed consolidated balance sheets at March 31, 2023 and September 30, 2022. Not included in these tables are cash deposits of $114.3 million and $113.9 million at March 31, 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 March 31, 2023 and September 30, 2022.