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 |