Stock-based compensation and warrants - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 31, 2014	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increased number of issuance of awards under the 2013 Plan	960
Number of shares available for issuance		539	539
Expenses related to consulting service			$ 168
Stock options held by former employees		123	123
Incremental value on option valuation			643
Stock option share exercised			844
Proceed from option share exercised			2,310
Warrants outstanding		338	338	338
Warrants exercised		0	0
Warrants cancelled or expired		0	0
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock- based compensation expense related to unvested stock options and restricted stock awards		21,054	21,054
Expected period for stock option			2 years 9 months 18 days
Restricted Stock Units R S U [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock- based compensation expense related to unvested stock options and restricted stock awards		4,638	4,638
Expected period for stock option			1 year 9 months 18 days
Restricted Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of stock in exchange of consulting services			2
Expenses related to consulting service			$ 42
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Initial issuance of common stock		238	238