Short-term Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 26,606	$ 36,192
Short-term Investments, Unrealized Losses	(144)	(55)
Short-term Investments, Estimated Fair Value	26,462	36,137
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	17,503	22,829
Short-term Investments, Unrealized Losses	(109)	(31)
Short-term Investments, Estimated Fair Value	17,394	22,798
Government bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	9,103	13,363
Short-term Investments, Unrealized Losses	(35)	(24)
Short-term Investments, Estimated Fair Value	$ 9,068	$ 13,339