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Share-Based Compensation - Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions (Details)	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020
Risk-free interest rate				1.50%
Expected dividend yield			0.00%	0.00%
Expected volatility			146.10%
Minimum [Member]
Risk-free interest rate			0.07%
Expected life (in years)			6 months	1 year 3 months 19 days
Expected volatility				109.80%
Maximum [Member]
Risk-free interest rate			0.08%
Expected life (in years)			9 months	1 year 4 months 24 days
Expected volatility				130.10%
Employee Stock Option [Member]
Risk-free interest rate	0.60%	1.70%	0.60%	1.70%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility	136.50%		136.50%
Employee Stock Option [Member] | Minimum [Member]
Expected life (in years)	5 years 6 months	5 years 6 months	5 years 6 months	5 years 6 months
Expected volatility		127.60%		127.60%
Employee Stock Option [Member] | Maximum [Member]
Expected life (in years)	5 years 8 months 12 days	5 years 8 months 12 days	5 years 8 months 12 days	5 years 8 months 12 days
Expected volatility		128.20%		128.20%
Performance Stock Options [Member]
Risk-free interest rate	1.20%	2.30%	1.20%	2.30%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected life (in years)	10 years	10 years	10 years	10 years
Expected volatility		115.00%		115.00%
Performance Stock Options [Member] | Minimum [Member]
Expected volatility	76.00%		76.00%
Performance Stock Options [Member] | Maximum [Member]
Expected volatility	136.50%		136.50%

X

- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ 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
-Subparagraph (f)(2)(iii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ 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
-Subparagraph (f)(2)(ii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ 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
-Subparagraph (f)(2)(iv)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ 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=120381028&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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