Note 4 - Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, plant and equipment, net	$ 164,205	$ 161,662
Computer Equipment [Member]
Property, plant and equipment, gross	487	487
Furniture and Fixtures [Member]
Property, plant and equipment, gross	464	464
Leasehold Improvements [Member]
Property, plant and equipment, gross	101	101
Excluding Construction in Progress [Member]
Property, plant and equipment, gross	1,052	1,052
Less: accumulated depreciation	(708)	(660)
Property, plant and equipment, net	344	392
Construction in Progress [Member]
Property, plant and equipment, gross	163,861	161,270
Construction in Progress [Member] \| Rio Grande [Member]
Property, plant and equipment, gross	142,760	140,253
Construction in Progress [Member] \| Rio Bravo [Member]
Property, plant and equipment, gross	$ 21,101	$ 21,017

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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