Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Dec. 31, 2023	Sep. 30, 2023
Assets:
Marketable securities		$ 36,955	$ 33,014
Cash deposits		120,200	113,200
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	40,253	23,621
Marketable securities	[2]	36,955	33,014
Total		77,208	56,635
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	40,253	23,621
Marketable securities	[2]	36,955	33,014
Total		$ 77,208	$ 56,635

[1] Included in cash and cash equivalents on our condensed consolidated balance sheets at December 31, 2023 and September 30, 2023. Not included in these tables are cash deposits of $120.2 million and $113.2 million at December 31, 2023 and September 30, 2023, 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 December 31, 2023 and September 30, 2023.