Loan facility - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Mar. 28, 2014	Oct. 30, 2013	Oct. 23, 2013
Line of Credit Facility [Line Items]
Term loan, amount borrowed		$ 2,500,000
Term loan repayment	2,609,844
Silicon Valley Bank [Member]
Line of Credit Facility [Line Items]
Term loan facility with Silicon Valley Bank					4,000,000
Term loan, amount borrowed				2,500,000
Warrants expire	2023
Term loan repayment			2,609,844
Term loan, loss on extinguishment of debt			$ 213,511
Silicon Valley Bank [Member] | Warrants to Purchase Series C Preferred Stock [Member]
Line of Credit Facility [Line Items]
Warrants to purchase per share					$ 10.56
Warrants to purchase shares of stock, shares					11,363
Silicon Valley Bank [Member] | Warrants to Purchase Common Stock [Member]
Line of Credit Facility [Line Items]
Warrants exercisable	11,363