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Fair Value of Financial Assets and Liabilities - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands | Jan. 31, 2016 | Apr. 30, 2015
--- | --- | ---
Cash and Cash Equivalents [Line Items] |  |
Total cash and cash equivalents | $ 57,944 | $ 54,041
Municipal debt securities |  |
Cash and Cash Equivalents [Line Items] |  |
Total cash and cash equivalents | 0 | 102
Corporate debt securities |  |
Cash and Cash Equivalents [Line Items] |  |
Total cash and cash equivalents | 0 | 256
Demand deposit accounts |  |
Cash and Cash Equivalents [Line Items] |  |
Total cash and cash equivalents | 53,041 | 49,977
Money market funds |  |
Cash and Cash Equivalents [Line Items] |  |
Total cash and cash equivalents | 462 | 2,831
Commercial paper |  |
Cash and Cash Equivalents [Line Items] |  |
Total cash and cash equivalents | 1,940 | 875
US government agencies debt securities |  |
Cash and Cash Equivalents [Line Items] |  |
Total cash and cash equivalents | $ 2,501 | $ 0

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