Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands		Sep. 30, 2022	Sep. 30, 2021
Assets:
Total		$ 43,829	$ 32,078
Cash
Assets:
Cash equivalents	[1]	19,314	194
Marketable securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	24,515	31,884
Active Markets for Identical Instruments (Level 1)
Assets:
Total		43,829	32,078
Active Markets for Identical Instruments (Level 1) | Cash
Assets:
Cash equivalents	[1]	19,314	194
Active Markets for Identical Instruments (Level 1) | Marketable securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	$ 24,515	$ 31,884

[1] Included in cash and cash equivalents on our consolidated balance sheets at September 30, 2022 and 2021. Not included in these tables are cash deposits of $113.9 million and $195.2 million at September 30, 2022 and 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 consolidated balance sheets at September 30, 2022 and 2021.