Short-term Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 36,541	$ 27,511
Short-term Investments, Unrealized Losses	(80)	(20)
Short-term Investments, Estimated Fair Value	36,461	27,491
Corporate bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	23,756	17,342
Short-term Investments, Unrealized Losses	(45)	(19)
Short-term Investments, Estimated Fair Value	23,711	17,323
Government bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	12,785	10,169
Short-term Investments, Unrealized Losses	(35)	(1)
Short-term Investments, Estimated Fair Value	$ 12,750	$ 10,168