Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands		Sep. 30, 2020	Sep. 30, 2019
Assets:
Total		$ 60,788	$ 49,123
Cash
Assets:
Cash equivalents	[1]	35,275	28,901
Marketable securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	25,513	20,222
Active Markets for Identical Instruments (Level 1)
Assets:
Total		60,788	49,123
Active Markets for Identical Instruments (Level 1) | Cash
Assets:
Cash equivalents	[1]	35,275	28,901
Active Markets for Identical Instruments (Level 1) | Marketable securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	$ 25,513	$ 20,222

[1] Included in cash and cash equivalents on our consolidated balance sheets at September 30, 2020 and 2019. Not included in this table are cash deposits of $122.1 million and $77.5 million at September 30, 2020 and 2019, 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 long-term marketable securities on our consolidated balance sheets at September 30, 2020 and 2019.