Share-Based Payments - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018	Apr. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 335,000	$ 152,000	$ 498,000	$ 848,000
Option modification charge		$ 57,000
Unrecognized compensation cost	$ 970,000		$ 970,000
Period for recognition			4 years 3 months
Weighted-average grant date fair value (in usd per share)	$ 5.76	$ 2.32	$ 6.03	$ 1.95
Warrants outstanding (in shares)	1,671,440		1,671,440		2,004,284

The number of share warrants outstanding in connection with the financing arrangement.

No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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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.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
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