Income Taxes - Aggregate Changes in Balance of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Income Tax Disclosure [Abstract]
Beginning unrecognized tax benefits	$ 3,619	$ 2,157	$ 1,729
Tax positions taken in prior periods:
Gross increases	88	883	0
Gross decreases	(42)	0	(14)
Tax positions taken in current period:
Gross increases	528	579	442
Gross decreases	0	0	0
Lapse of statute of limitations	0	0	0
Ending unrecognized tax benefits	$ 4,193	$ 3,619	$ 2,157

Tax Positions Taken In Current Period [Abstract]

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Tax Positions Taken In Prior Periods [Abstract]

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Amount of unrecognized tax benefits.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=SL6600010-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Unrecognized Tax Benefit
-URI http://asc.fasb.org/extlink&oid=6527854

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Amount of decrease in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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