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Fair Value of Financial Assets and Liabilities - Summary of Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands | Jan. 31, 2016 | Apr. 30, 2015
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | $ 57,944 | $ 54,041
Short-term investments: | 50,975 | 52,730
Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 4,903 | 4,064
Short-term investments: | 50,975 | 52,730
Total assets | 55,878 | 56,794
Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 2,963 | 2,831
Short-term investments: | 33,804 | 28,808
Total assets | 36,767 | 31,639
Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 1,940 | 1,233
Short-term investments: | 17,171 | 23,922
Total assets | 19,111 | 25,155
Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
Total assets | 0 | 0
Certificates of deposit | Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 7,809 | 4,004
Certificates of deposit | Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
Certificates of deposit | Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 7,809 | 4,004
Certificates of deposit | Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
Municipal bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 102
Municipal bonds | Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 102
Short-term investments: | 391 | 4,565
Municipal bonds | Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
Municipal bonds | Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 102
Short-term investments: | 391 | 4,565
Municipal bonds | Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
Commercial paper | Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 1,940 | 875
Short-term investments: | 3,442 | 6,273
Commercial paper | Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
Commercial paper | Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 1,940 | 875
Short-term investments: | 3,442 | 6,273
Commercial paper | Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
U.S. Treasury securities | Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 8,761 | 11,803
U.S. Treasury securities | Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 8,761 | 11,803
U.S. Treasury securities | Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
U.S. Treasury securities | Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Short-term investments: | 0 | 0
US government agencies debt securities | Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 2,501 | 0
Short-term investments: | 25,043 | 17,005
US government agencies debt securities | Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 2,501 | 0
Short-term investments: | 25,043 | 17,005
US government agencies debt securities | Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
US government agencies debt securities | Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
Corporate debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 256
Corporate debt securities | Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 256
Short-term investments: | 5,529 | 9,080
Corporate debt securities | Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
Corporate debt securities | Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 256
Short-term investments: | 5,529 | 9,080
Corporate debt securities | Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Short-term investments: | 0 | 0
Money market funds | Fair value, measurements, recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 462 | 2,831
Money market funds | Fair value, measurements, recurring | Fair value, inputs, level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 462 | 2,831
Money market funds | Fair value, measurements, recurring | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | 0 | 0
Money market funds | Fair value, measurements, recurring | Fair value, inputs, level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash equivalents: | $ 0 | $ 0

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph g -Article 7 + Details
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