Note 10 - Asset Retirement Obligations - Estimated Amounts and Timing of Cash Flows and Assumptions Used for ARO Estimates (Details)	Jan. 31, 2019 USD ($)	Jul. 31, 2018 USD ($)
Undiscounted amount of estimated cash flows	$ 7,275,504	$ 7,275,504
Measurement Input, Expected Term [Member] | Minimum [Member]
Payable in years	5	5
Measurement Input, Expected Term [Member] | Maximum [Member]
Payable in years	17	17
Measurement Input, Inflation Rate [Member] | Minimum [Member]
Payable in years	0.0137	0.0137
Measurement Input, Inflation Rate [Member] | Maximum [Member]
Payable in years	2.14	2.14
Measurement Input, Discount Rate [Member] | Minimum [Member]
Payable in years	0.0548	0.0548
Measurement Input, Discount Rate [Member] | Maximum [Member]
Payable in years	6.4	6.4