Note 10 - Asset Retirement Obligations - Estimated Amounts and Timing of Cash Flows and Assumptions Used for ARO Estimates (Details)	Oct. 31, 2019 USD ($) yr	Jul. 31, 2019 USD ($) yr
Undiscounted amount of estimated cash flows | $	$ 8,221,018
Maximum [Member]
Undiscounted amount of estimated cash flows | $	$ 8,221,018	$ 8,221,018
Maximum [Member] | Measurement Input, Expected Term [Member]
Asset retirement obligations, measurement input (Year) | yr	21	21
Maximum [Member] | Measurement Input, Inflation Rate [Member]
Asset retirement obligations, measurement input (Year)	0.0217	0.0217
Maximum [Member] | Measurement Input, Discount Rate [Member]
Asset retirement obligations, measurement input (Year)	0.0596	0.0596
Minimum [Member] | Measurement Input, Expected Term [Member]
Asset retirement obligations, measurement input (Year) | yr	9	9
Minimum [Member] | Measurement Input, Inflation Rate [Member]
Asset retirement obligations, measurement input (Year)	0.0156	0.0156
Minimum [Member] | Measurement Input, Discount Rate [Member]
Asset retirement obligations, measurement input (Year)	0.055	0.055