Note 1 - Nature of Operations (Details Textual) - USD ($)	9 Months Ended	12 Months Ended
	Apr. 30, 2019	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2014	Dec. 05, 2018	Oct. 31, 2018	Oct. 03, 2018	Apr. 30, 2018
Revenue from Contract with Customer, Including Assessed Tax	$ 0	$ 0	$ 0	$ 0	$ 0
Shares Issued, Price Per Share	$ 1.33
Stock Issued During Period, Value, New Issues	$ 15,990,962
Working Capital	21,500,000
Cash and Cash Equivalents, at Carrying Value, Ending Balance	6,093,098	6,926,523							$ 11,223,448
Short-term Investments, Total	14,858,126
Long-term Debt, Gross	20,000,000	20,000,000				$ 20,000,000
Long-term Debt, Current Maturities, Total		$ 10,000,000					$ 15,000,000
Entity Incorporation, Date of Incorporation	May 16, 2003
Equity Financing [Member]
Stock Issued During Period, Shares, New Issues	12,613,049
Shares Issued, Price Per Share	$ 1.60							$ 1.60
Stock Issued During Period, Value, New Issues	$ 20,200,000
Proceeds from Stock Options and Warrants Exercised	$ 4,900,000