Property, plant and equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 20,302	$ 18,908
Accumulated depreciation	12,766	11,021
Total	7,536	7,887
Land
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	535	535
Buildings
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 830	830
Property, Plant and Equipment, Useful Life	39 years
Building improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 810	776
Property, Plant and Equipment, Useful Life	39 years
Equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 13,206	12,429
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Equipment under capital lease
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 234	100
Equipment under capital lease | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Equipment under capital lease | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Vehicles
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,311	1,281
Property, Plant and Equipment, Useful Life	5 years
Lab and computer equipment, software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 2,499	2,377
Lab and computer equipment, software | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Lab and computer equipment, software | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Furniture & fixtures
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 276	265
Furniture & fixtures | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	8 years
Furniture & fixtures | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 110	90
Property, Plant and Equipment, Useful Life	3 years
Equipment under construction
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 491	$ 225