Property, plant, and equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 524,000	$ 470,000
Lab and computer equipment software acquired	995,000
Issuance of common stock in connection with asset purchase	$ 600,000