Note 6 - Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Property, Plant and Equipment [Table Text Block]

	Useful Life				December 31,
	(in years)				2019			2018
Luverne retrofit asset			20		$	70,820		$	70,842
Plant machinery and equipment			10			17,413			16,285
Site improvements			10			7,054			7,055
Lab equipment, furniture and fixtures and vehicles			5			6,393			6,574
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			2,542
Computer, office equipment and software		3	to	6		2,034			2,335
Construction in progress			—			7,710			3,478
						120,087			115,251
Less accumulated depreciation and amortization						(53,391	)		(47,789	)
Property, plant and equipment, net					$	66,696		$	67,462

Schedule of Depreciation and Amortization Expense [Table Text Block]

	Year Ended December 31,
	2019		2018
Cost of goods sold	$	6,282	$	6,250
Operating expenses		210		267
Total depreciation and amortization	$	6,492	$	6,517