Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 9,513	$ 25,553
Short-term Investments, Unrealized Gains	7
Short-term Investments, Unrealized Losses	(25)	(82)
Short-term Investments, Estimated Fair Value	9,495	25,471
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	6,289	17,851
Short-term Investments, Unrealized Losses	(25)	(60)
Short-term Investments, Estimated Fair Value	6,264	17,791
Government bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	3,224	7,702
Short-term Investments, Unrealized Gains	7
Short-term Investments, Unrealized Losses		(22)
Short-term Investments, Estimated Fair Value	$ 3,231	$ 7,680