Note 6 - Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

Property, Plant and Equipment [Table Text Block]

	Useful Life				December 31,
	(in years)				2020			2019
Luverne retrofit asset			20		$	70,820		$	70,820
Plant machinery and equipment			10			17,374			17,413
Site improvements			10			7,157			7,054
Lab equipment, furniture and fixtures and vehicles			5			6,396			6,393
Demonstration plant			2			3,597			3,597
Buildings			10			2,543			2,543
Leasehold improvements, pilot plant, land and support equipment		2	to	5		2,523			2,523
Computer, office equipment and software		3	to	6		1,983			2,034
Construction in progress			—			13,132			7,710
Total Property, plant and equipment						125,525			120,087
Less accumulated depreciation and amortization						(59,117	)		(53,391	)
Property, plant and equipment, net					$	66,408		$	66,696

Schedule of Depreciation and Amortization Expense [Table Text Block]

	Year Ended December 31,
	2020		2019
Cost of goods sold	$	5,669	$	6,282
Operating expenses		212		210
Total depreciation and amortization	$	5,881	$	6,492