Summary of Significant Accounting Policies - Income Tax (Details) - USD ($)	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Accounting Policies [Abstract]
Federal statutory income tax rate, percent	21.00%	21.00%	21.00%
Income tax expense	$ 0	$ 0	$ (2,827,000)