Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands		Sep. 30, 2024	Sep. 30, 2023
Equity Securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI		$ 45,289	$ 33,014
Fair Value, Measurements, Recurring
Assets:
Total		53,188	56,635
Fair Value, Measurements, Recurring | Cash
Assets:
Cash equivalents	[1]	7,899	23,621
Fair Value, Measurements, Recurring | Equity Securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	45,289	33,014
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Total		53,188	56,635
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1) | Cash
Assets:
Cash equivalents	[1]	7,899	23,621
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1) | Equity Securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	$ 45,289	$ 33,014

[1] Included in cash and cash equivalents on our consolidated balance sheets at September 30, 2024 and 2023. Not included in these tables are cash deposits of $142.8 million and $113.2 million at September 30, 2024 and 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 consolidated balance sheets at September 30, 2024 and 2023.