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v3.20.4

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% |

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- 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 + Details
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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 + Details
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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 + Details
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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 -Subparagraph (f)(2)(i) -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 + Details
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