Loan facility - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended	0 Months Ended		3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 28, 2014 Silicon Valley Bank [Member]	Oct. 30, 2013 Silicon Valley Bank [Member]	Mar. 31, 2014 Silicon Valley Bank [Member]	Dec. 31, 2013 Silicon Valley Bank [Member]	Oct. 23, 2013 Silicon Valley Bank [Member]	Oct. 23, 2013 Silicon Valley Bank [Member] Warrants to Purchase Series C Convertible Preferred Stock [Member]	Mar. 31, 2014 Silicon Valley Bank [Member] Warrants to Purchase Common Stock [Member]
Line of Credit Facility [Line Items]
Term loan facility with Silicon Valley Bank							$ 4,000,000
Term loan, amount borrowed		2,500,000		2,500,000
Term loan borrowing capacity, available upon receiving Phase 2 top-line data results						1,500,000
Warrants to purchase per share								10.56
Warrants to purchase shares of stock, shares								11,363
Warrants exercisable									11,363
Warrant expire					2023
Term loan interest rate					5.25%
Term loan, periodic principal repayments					83,000
Term loan, maturity date					Mar. 31, 2017
Term loan, payment terms					The term loan principal is repayable in monthly installments approximately $83,000 commencing October 2014
Term loan repayment	2,609,844		2,609,844
Term loan, loss on extinguishment of debt			$ 213,511