Reconciliation of Federal Statutory Income Tax (Detail)	12 Months Ended
May 31, 2020	May 31, 2019	May 31, 2018
Schedule Of Income Taxes [Line Items]
Income tax provision at statutory rate:	21.00%	21.00%	28.60%
State income taxes net	0.00%	0.00%	0.00%
Rate change	0.00%	0.00%	(34.80%)
Loss on debt extinguishment	0.00%	(0.50%)	0.00%
Derivative gain (loss)	(1.60%)	0.60%	1.00%
Valuation allowance release from asset acquisition	0.00%	4.80%	0.00%
Non-deductible debt issuance costs	(0.10%)	0.00%	(0.20%)
Non-deductible interest on convertible notes	(1.20%)	(0.30%)	(0.10%)
Inducement interest expense	(1.30%)	(0.10%)	(2.00%)
Other	(0.30%)	0.00%	(1.10%)
Miscellaneous	0.00%	0.00%	(0.10%)
Current year credits generated	0.00%	0.00%	4.40%
Credit carry forward generated (released)	(0.10%)	(3.80%)	4.10%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amortization, Percent	(0.30%)	0.00%	0.00%
Effective Income Tax Rate Reconciliation Non Deductible Expense IRC 162 limitation	(2.40%)	0.00%	0.00%
Stock compensation in excess of ASC 718	3.20%	0.00%	0.00%
Non-deductible legal settlement expense	(3.80%)	0.00%	0.00%
Valuation allowance	(13.10%)	(16.90%)	0.30%
Total	0.00%	4.80%	0.00%

Effective Income Tax Rate Reconciliation, Derivative Gain Loss, Percent

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Effective Income Tax Rate Reconciliation Inducement Charge

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Effective Income Tax Rate Reconciliation Loss On Debt Conversion

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Effective income tax rate reconciliation non deductible expense IRC 162 limitation.

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Effective income tax rate reconciliation nondeductible expense debt issuance costs percent.

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Effective Income Tax Rate Reconciliation Nondeductible Expense Interest

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Effective income tax rate reconciliation nondeductible legal settlement expense.

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Effective income tax rate reconciliation tax credit carryforward.

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Represents Effective Income Tax Reconciliation Valuation Allowance From Asset Acquisition.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage 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 changes in the valuation allowance for deferred tax assets.

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Percentage 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 applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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Percentage of the difference, between reported income tax expense (benefit) and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, that is attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority interest income (expense), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, change in enacted tax rate, prior year income taxes, change in deferred tax asset valuation allowance, and other adjustments.

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Percentage 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 applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage 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 tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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