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Equity Plans - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jul. 31, 2016 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Common stock reserved for issuance |  | 2,558,157 | 6,579,361 |
Aggregate intrinsic value of options exercised |  | $ 169,000 |  |
Options, weighted-average grant-date fair value |  | $ 8.20 | $ 0.69 | $ 0.82
Expected dividend yield |  | 0.00% | 0.00% | 0.00%
Stock-based compensation expense |  | $ 2,130,000 | $ 99,000 | $ 42,000
Total unrecognized stock-based compensation costs related to stock options |  | $ 12,600,000 |  |
Period of unrecognized stock-based compensation costs to be recognized |  | 3 years 1 month 13 days |  |
2016 Equity Incentive Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Additional vesting years | 3 years |  |  |
Common stock reserved for issuance | 1,200,000 | 1,200,000 |  |
Vesting percentage of requisite service period | 25.00% |  |  |
2016 Equity Incentive Plan [Member] | Maximum [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Expiration period | 10 years |  |  |
Exercise price as a percentage of the fair market value of common stock on grant date | 100.00% |  |  |
2016 Equity Incentive Plan [Member] | Minimum [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Exercise price as a percentage of the fair market value for option holding more than 10% total combined voting power | 110.00% |  |  |
Minimum percentage of voting right to grant stock option | 10.00% |  |  |
2016 Employee Stock Purchase Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Common stock reserved for issuance | 150,000 |  |  |
Expected dividend yield |  | 0.00% |  |
Percentage of discount from fair market value of common stock on offering date | 85.00% |  |  |
Maximum percentage of outstanding stock issuance | 1.00% |  |  |
Maximum number of outstanding stock issuance | 300,000 |  |  |
Maximum period for additional outstanding stock issuance | 10 years |  |  |
2016 Employee Stock Purchase Plan [Member] | Maximum [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Maximum percentage of payroll deductions on eligible compensation | 15.00% |  |  |
2007 Stock Option and Incentive Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Expiration period |  | 10 years |  |
Additional vesting years |  | 4 years |  |
Cliff vesting period |  | 1 year |  |
Non-employee Consultants [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options granted |  | 59,647 | 4,816 | 11,805
Stock-based compensation expense |  | $ 505,000 | $ 15,000 | $ 5,000

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