Property, plant and equipment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 22,331	$ 21,983
Accumulated depreciation	14,913	14,451
Total	7,418	7,532
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	$ 873	873
Property, Plant and Equipment, Useful Life	39 years
Equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 13,516	13,423
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	$ 188	248
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	$ 1,337	1,360
Property, Plant and Equipment, Useful Life	5 years
Lab and computer equipment, software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 2,726	2,652
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	$ 288	289
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	$ 119	119
Property, Plant and Equipment, Useful Life	3 years
Equipment under construction
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,919	$ 1,654