Fair Value Measurement of Company's Short-term Investments and Derivative Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Sep. 30, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term Investments, Estimated Fair Value	$ 27,254	$ 18,112
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	27,243	18,094
Fair Value, Measurements, Recurring | Corporate bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term Investments, Estimated Fair Value	17,672	15,161
Fair Value, Measurements, Recurring | Government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term Investments, Estimated Fair Value	9,582	2,951
Fair Value, Measurements, Recurring | Foreign Currency Forward Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net Derivatives	(11)	(18)
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	27,254	18,112
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term Investments, Estimated Fair Value	17,672	15,161
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term Investments, Estimated Fair Value	9,582	2,951
Fair Value, Measurements, Recurring | Significant Other Observable (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	(11)	(18)
Fair Value, Measurements, Recurring | Significant Other Observable (Level 2) | Foreign Currency Forward Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net Derivatives	$ (11)	$ (18)