Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Going concern thru intangibles (Detail)

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Summary of Significant Accounting Policies - Going concern thru intangibles (Detail) - USD ($)
 3 Months Ended 9 Months Ended
Feb. 28, 2021
Nov. 30, 2020
Aug. 31, 2020
Feb. 29, 2020
Nov. 30, 2019
Aug. 31, 2019
Feb. 28, 2021
Feb. 29, 2020
May 31, 2020
Accounting Policies [Abstract]                  
Net loss $ 43,985,000 $ 34,966,000 $ 30,832,000 $ 35,768,000 $ 14,860,000 $ 16,164,000 $ 109,783,000 $ 66,792,000  
Accumulated deficit 465,983,000           465,983,000   $ 354,711,000
Balance in excess of federally insured limits 14,000,000.0           14,000,000.0   $ 14,000,000.0
Intangible asset impairment charges $ 10.0     $ 0     $ 10.0 $ 0