Property, Plant and Equipment by Classification (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property, plant and equipment	$ 110,844	$ 110,222
Less accumulated depreciation and amortization	(36,306)	(34,630)
Property, plant and equipment, net	74,538	75,592
Construction in progress
Property Plant And Equipment [Line Items]
Total property, plant and equipment	$ 574	293
Plant machinery and equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Total property, plant and equipment	$ 15,574	15,397
Site improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Total property, plant and equipment	$ 7,050	7,050
Luverne retrofit asset
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	20 years
Total property, plant and equipment	$ 70,842	70,791
Lab equipment, furniture and fixtures and vehicles
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Total property, plant and equipment	$ 6,508	6,431
Demonstration plant
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	2 years
Total property, plant and equipment	$ 3,597	3,597
Buildings
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Total property, plant and equipment	$ 2,543	2,543
Computer, office equipment and software
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Total property, plant and equipment	$ 1,621	1,594
Leasehold improvements, pilot plant, land and support equipment
Property Plant And Equipment [Line Items]
Total property, plant and equipment	$ 2,535	$ 2,526
Leasehold improvements, pilot plant, land and support equipment | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	2 years
Leasehold improvements, pilot plant, land and support equipment | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	5 years