Note 6 - Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, plant and equipment, net	$ 161,662	$ 134,591
Computer Equipment [Member]
Property, plant and equipment, gross	487	487
Furniture and Fixtures [Member]
Property, plant and equipment, gross	464	471
Leasehold Improvements [Member]
Property, plant and equipment, gross	101	547
Excluding Construction in Progress [Member]
Property, plant and equipment, gross	1,052	1,505
Less: accumulated depreciation	(660)	(793)
Property, plant and equipment, net	392	712
Construction in Progress [Member]
Property, plant and equipment, gross	161,270	133,879
Construction in Progress [Member] \| Rio Grande [Member]
Property, plant and equipment, gross	140,253	121,081
Construction in Progress [Member] \| Rio Bravo [Member]
Property, plant and equipment, gross	$ 21,017	$ 12,798

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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