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Fair Value of Company's Short-term Investments, Contingemt Earn-Out Liability and Foreign Currency Forward Contracts (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Sep. 30, 2018 | Sep. 30, 2017
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Contingent earn-out liability | $ (7,713) |
Total | 17,488 | $ 36,137
Corporate bonds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Short-term Investments, Estimated Fair Value | 17,791 | 22,798
Government bonds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Short-term Investments, Estimated Fair Value | 7,680 | 13,339
Foreign Currency Forward Contracts |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Net Derivatives | (270) |
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total | 25,471 | 36,137
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 | 17,791 | 22,798
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 | 7,680 | $ 13,339
Significant Other Observable (Level 2) |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total | (270) |
Significant Other Observable (Level 2) | Foreign Currency Forward Contracts |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Net Derivatives | (270) |
Fair Value, Inputs, Level 3 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Contingent earn-out liability | (7,713) |
Total | $ (7,713) |

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- Definition Fair value of contingent consideration in a business combination that is classified in shareholders' equity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 + Details
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