Summary of Significant Accounting Policies - Antidilutive Securities (Detail) - shares shares in Thousands	6 Months Ended
	Nov. 30, 2021	Nov. 30, 2020
Stock options, warrants & unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	73,223	82,796
Convertible Debt Securities
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	12,000	12,000
Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	34,089	31,490