Short-term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 25,553	$ 36,195
Short-term Investments, Unrealized Losses	(82)	(58)
Short-term Investments, Estimated Fair Value	25,471	36,137
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	17,851	22,832
Short-term Investments, Unrealized Losses	(60)	(34)
Short-term Investments, Estimated Fair Value	17,791	22,798
Government bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	7,702	13,363
Short-term Investments, Unrealized Losses	(22)	(24)
Short-term Investments, Estimated Fair Value	$ 7,680	$ 13,339