Note 13 - Stock-based Compensation - Summary of Stock Options Outstanding and Exercisable (Details) - $ / shares	12 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Options Outstanding (in shares)	15,738,350	14,911,625	12,260,500	12,105,858
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 1.30	$ 1.41	$ 1.33	$ 1.34
Options Outstanding, Weighted Average Remaining Contractual Term (Year)	2 years 197 days
Options Exercisable (in shares)	12,427,750
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 1.34
Options Exercisable, Weighted Average Remaining Contractual Term (Year)	1 year 98 days
Exercise Price Range 1 [Member]
Range of Exercise Prices, Lower Limit (in dollars per share)	$ 0.93
Range of Exercise Prices, Upper Limit (in dollars per share)	$ 0.99
Options Outstanding (in shares)	3,643,100
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 0.94
Options Outstanding, Weighted Average Remaining Contractual Term (Year)	6 years 25 days
Options Exercisable (in shares)	1,766,750
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 0.94
Options Exercisable, Weighted Average Remaining Contractual Term (Year)	1 year 328 days
Exercise Price Range 2 [Member]
Range of Exercise Prices, Lower Limit (in dollars per share)	$ 1
Range of Exercise Prices, Upper Limit (in dollars per share)	$ 1.49
Options Outstanding (in shares)	9,465,000
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 1.28
Options Outstanding, Weighted Average Remaining Contractual Term (Year)	354 days
Options Exercisable (in shares)	8,989,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 1.28
Options Exercisable, Weighted Average Remaining Contractual Term (Year)	310 days
Exercise Price Range 3 [Member]
Range of Exercise Prices, Lower Limit (in dollars per share)	$ 1.50
Range of Exercise Prices, Upper Limit (in dollars per share)	$ 3.75
Options Outstanding (in shares)	2,630,250
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 1.86
Options Outstanding, Weighted Average Remaining Contractual Term (Year)	3 years 105 days
Options Exercisable (in shares)	1,672,000
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 2.06
Options Exercisable, Weighted Average Remaining Contractual Term (Year)	2 years 324 days