Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Dec. 31, 2024	Sep. 30, 2024
Assets:
Marketable securities		$ 45,925	$ 45,289
Cash deposits		183,500	142,800
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	740	7,899
Marketable securities	[2]	45,925	45,289
Total		46,665	53,188
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	740	7,899
Marketable securities	[2]	45,925	45,289
Total		$ 46,665	$ 53,188

[1] Included in cash and cash equivalents on our condensed consolidated balance sheets at December 31, 2024 and September 30, 2024. Not included in these tables are cash deposits of $183.5 million and $142.8 million at December 31, 2024 and September 30, 2024, 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, 2024 and September 30, 2024.