Note 11 - Concentrations of Credit Risk - Concentrations of Credit Risk (Details) - Customer Concentration Risk [Member]	3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017	May 31, 2017
Sales Revenue, Net [Member]
Concentration risk, percentage	76.00%	88.00%	85.00%	68.00%
Sales Revenue, Net [Member] | Customer One [Member]
Concentration risk, percentage	48.00%	88.00%	67.00%	22.00%
Sales Revenue, Net [Member] | Customer Two [Member]
Concentration risk, percentage	28.00%		18.00%	46.00%
Accounts Receivable [Member]
Concentration risk, percentage			83.00%		91.00%
Accounts Receivable [Member] | Customer One [Member]
Concentration risk, percentage			43.00%		50.00%
Accounts Receivable [Member] | Customer Two [Member]
Concentration risk, percentage			40.00%		41.00%