Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Assets:
Available-for-sale securities	$ 36,969	$ 53,518
Fair Value, Measurements, Recurring
Assets:
Available-for-sale securities	36,969	53,518
Foreign exchange contracts	17	170
Total Assets	53,150	104,260
Liabilities:
Foreign exchange contracts	340	177
Total Liabilities	340	177
Fair Value, Measurements, Recurring \| Cash equivalents
Assets:
Cash equivalents	16,164	50,572
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Recurring
Assets:
Total Assets	6,188	50,572
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value, Measurements, Recurring \| Cash equivalents
Assets:
Cash equivalents	6,188	50,572
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring
Assets:
Cash equivalents	10,000
Available-for-sale securities	36,969	53,518
Foreign exchange contracts	17	170
Total Assets	46,962	53,688
Liabilities:
Foreign exchange contracts	340	177
Total Liabilities	340	$ 177
Significant Other Observable Inputs (Level 2) \| Fair Value, Measurements, Recurring \| Cash equivalents
Assets:
Cash equivalents	$ 9,976

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps.

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Fair value portion of liability contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward (delivery or nondelivery) contracts, and swaps entered into.

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Fair value of financial and nonfinancial obligations.

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