Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands		Sep. 30, 2019	Sep. 30, 2018
Assets:
Total		$ 49,123	$ 36,472
Cash
Assets:
Cash equivalents	[1]	28,901	18,413
Marketable securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	20,222	18,059
Active Markets for Identical Instruments (Level 1)
Assets:
Total		49,123	36,472
Active Markets for Identical Instruments (Level 1) | Cash
Assets:
Cash equivalents	[1]	28,901	18,413
Active Markets for Identical Instruments (Level 1) | Marketable securities
Assets:
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	$ 20,222	$ 18,059

[1] Included in cash and cash equivalents on our balance sheet at September 30, 2019 and 2018. Not included in this table are cash deposits of $77.5 million and $71.6 million at September 30, 2019 and 2018, 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, 2019 and 2018.