| Note 5 - Asset Retirement Obligations (Tables) | 9 Months Ended | ||||||||||||||||||||||||||||||||||||||||
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| Sep. 30, 2020 | |||||||||||||||||||||||||||||||||||||||||
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| Schedule of Change in Asset Retirement Obligation [Table Text Block] | 
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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- References No definition available. 
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