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Income Taxes - Summary of Difference Between Tax Derived by Applying Federal Statutory Income Tax Rate (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
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Apr. 30, 2016 | Jan. 31, 2016 | Oct. 31, 2015 | Jul. 31, 2015 | Apr. 30, 2015 | Jan. 31, 2015 | Oct. 31, 2014 | Jul. 31, 2014 | Apr. 30, 2016 | Apr. 30, 2015 | Apr. 30, 2014
Income Tax Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
U.S. federal taxes at statutory rate |  |  |  |  |  |  |  |  | $ (8,603) | $ (11,257) | $ (18,138)
State tax provision |  |  |  |  |  |  |  |  | (625) | (923) | (1,510)
Foreign tax rate differentials |  |  |  |  |  |  |  |  | (108) | (206) | (123)
Research and development credit |  |  |  |  |  |  |  |  | (1,473) | (1,972) | (1,201)
Stock options |  |  |  |  |  |  |  |  | 3,480 | 506 | 1,608
Nondeductible legal expenses |  |  |  |  |  |  |  |  | 0 | 200 | 5,796
Permanent differences and other |  |  |  |  |  |  |  |  | 0 | (8) | (1,389)
Return to provision adjustments |  |  |  |  |  |  |  |  | 9 | 0 | 0
Change in valuation allowance |  |  |  |  |  |  |  |  | 7,358 | 13,714 | 14,457
Provision for (benefit from) income taxes | $ 165 | $ (163) | $ 124 | $ (88) | $ (540) | $ 324 | $ 258 | $ 12 | $ 38 | $ 54 | $ (500)

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- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32639-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Income Tax Expense (or Benefit) -URI http://asc.fasb.org/extlink&oid=6515339 + Details
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- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32698-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=75116654&loc=d3e32123-109318 + Details
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- Definition The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(h)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32698-109319 + Details
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- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible equity-based compensation costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32698-109319 + Details
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