Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Dec. 31, 2021	Sep. 30, 2021
Assets:
Marketable securities		$ 33,926	$ 31,884
Cash deposits		162,000	195,200
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	194	194
Marketable securities	[2]	33,926	31,884
Total		34,120	32,078
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	194	194
Marketable securities	[2]	33,926	31,884
Total		$ 34,120	$ 32,078

[1] Included in cash and cash equivalents on our condensed consolidated balance sheets at December 31, 2021 and September 30, 2021. Not included in these tables are cash deposits of $162.0 million and $195.2 million at December 31, 2021 and September 30, 2021, 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, 2021 and September 30, 2021.