Commitments and contingencies - Additional Information (Detail) (USD $)		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011 Research and Development Expense [Member]	Dec. 31, 2012 Selling General and Administrative Expenses [Member]
Commitments and Contingencies Disclosure [Line Items]
Settlement agreement amount	$ 32,000
Settlement of trade debt		$ 15,000	$ 546,000