Property, Plant and Equipment by Classification (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Total property, plant and equipment	$ 110,222	$ 104,680
Less accumulated depreciation and amortization	(34,630)	(27,903)
Property, plant and equipment, net	75,592	76,777
Construction in progress
Property Plant And Equipment [Line Items]
Total property, plant and equipment	$ 293	1,801
Plant machinery and equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Total property, plant and equipment	$ 15,397	14,113
Site improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Total property, plant and equipment	$ 7,050	7,039
Agri-Energy Retrofit asset
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	20 years
Total property, plant and equipment	$ 70,791	65,457
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	$ 6,431	6,389
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	$ 1,594	1,566
Leasehold improvements, pilot plant, land and support equipment
Property Plant And Equipment [Line Items]
Total property, plant and equipment	$ 2,526	$ 2,175
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