Common stock and preferred stock - Summary of Future Issuance of Common Stock Shares (Detail) - shares shares in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Capitalization [Line Items]
Common shares reserved for future issuance	4,472	4,805
Options to Purchase Common Stock [Member]
Schedule Of Capitalization [Line Items]
Common shares reserved for future issuance	3,532	3,652
Restricted Stock Units [Member]
Schedule Of Capitalization [Line Items]
Common shares reserved for future issuance	148	179
2013 Employee Stock Purchase Plan [Member]
Schedule Of Capitalization [Line Items]
Common shares reserved for future issuance	227	238
Warrants To Purchase Common Stock [Member]
Schedule Of Capitalization [Line Items]
Common shares reserved for future issuance		177
2013 Stock Option and Incentive Plan [Member]
Schedule Of Capitalization [Line Items]
Common shares reserved for future issuance	565	465
Acquisition holdback [Member]
Schedule Of Capitalization [Line Items]
Common shares reserved for future issuance		94