Note 6 - Commitments and Contingencies (Details Textual) $ in Millions	Mar. 31, 2019 USD ($)
Asset Retirement Obligation, Ending Balance	$ 12.9
Mine Reclamation and Closing Liability, Noncurrent	12.7
Take-or-pay Purchase Commitments [Member]
Purchase Commitment, Remaining Minimum Amount Committed	$ 2.7

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of a reclamation and mine closing liability that is associated with a legal obligation for the closure and reclamation of a mine including the removal of buildings, equipment, machinery and other physical remnants of mining, closure of tailings impoundments, leach pads and other mine features, and contouring, covering and revegetation of waste rock piles and other disturbed areas.

+ References

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-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.Y.Q2)
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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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