Reconciliation of Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - USD ($)	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 2,407,000	$ 1,324,000
Fair value adjustments			$ (3,855,000)
Ending Balance		2,407,000	1,324,000
Convertible notes [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value adjustments	(2,005,000)	(745,000)
Warrant [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value adjustments	11,547,000	(922,000)
Exercises	$ (11,949,000)
Investor Warrants Issued with Registered Direct Equity Offering
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Warrants issued			4,360,000
Placement Agent Warrants Issued with Registered Direct Equity Offering
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Warrants issued			$ 819,000
Inception date value of redemption provision - warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Warrants issued		$ 2,750,000