Stockholders' Equity - Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2017 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	18,691,478
2016 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	1,500,000
Warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	220,000
Stock options [Member] | Equity Incentive Plan 2008 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	622,192
Stock options [Member] | Equity Incentive Plan 2012 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	12,026,320
Stock options [Member] | 2016 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	1,372,960
Stock options [Member] | Incentive Award Agreements [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	2,088,212
Restricted stock units (RSUs) [Member] | Equity Incentive Plan 2012 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	2,152,972
Restricted stock units (RSUs) [Member] | Incentive Award Agreements [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	208,822