Note 10 - Asset Retirement Obligations - Estimated Amounts and Timing of Cash Flows and Assumptions Used for ARO Estimates (Details)	Apr. 30, 2019 USD ($) yr	Jul. 31, 2018 USD ($) yr
Undiscounted amount of estimated cash flows	$ 7,275,504
Minimum [Member]
Undiscounted amount of estimated cash flows		$ 7,275,504
Minimum [Member] | Measurement Input, Expected Term [Member]
Asset retirement obligations, measurement input | yr	5	5
Minimum [Member] | Measurement Input, Inflation Rate [Member]
Asset retirement obligations, measurement input	0.0137	0.0137
Minimum [Member] | Measurement Input, Discount Rate [Member]
Asset retirement obligations, measurement input	0.0548	0.0548
Maximum [Member]
Undiscounted amount of estimated cash flows		$ 7,275,504
Maximum [Member] | Measurement Input, Expected Term [Member]
Asset retirement obligations, measurement input | yr	17	17
Maximum [Member] | Measurement Input, Inflation Rate [Member]
Asset retirement obligations, measurement input	0.0214	0.0214
Maximum [Member] | Measurement Input, Discount Rate [Member]
Asset retirement obligations, measurement input	0.064	0.064