Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 32,191	$ 36,192
Short-term Investments, Unrealized Losses	(106)	(55)
Short-term Investments, Estimated Fair Value	32,085	36,137
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	21,739	22,829
Short-term Investments, Unrealized Losses	(67)	(31)
Short-term Investments, Estimated Fair Value	21,672	22,798
Government bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	10,452	13,363
Short-term Investments, Unrealized Losses	(39)	(24)
Short-term Investments, Estimated Fair Value	$ 10,413	$ 13,339