Property, plant and equipment (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 18,908us-gaap_PropertyPlantAndEquipmentGross	$ 14,662us-gaap_PropertyPlantAndEquipmentGross
Accumulated depreciation	11,021	10,126
Total	7,887us-gaap_PropertyPlantAndEquipmentNet	4,536us-gaap_PropertyPlantAndEquipmentNet
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	776	776
Property, Plant and Equipment, Useful Life	39 years
Equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	12,429	8,560
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	100	137
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	1,281	1,258
Property, Plant and Equipment, Useful Life	5 years
Lab and computer equipment, software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,377	2,210
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	265	249
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	90	70
Property, Plant and Equipment, Useful Life	3 years
Equipment under construction
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 225	$ 37

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.14)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 14

-Article 5

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- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 13

-Subparagraph a

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 8

-Article 7

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- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

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