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Stock Option Plans - Additional Information (Detail) - USD ($) | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Jul. 31, 2016 | Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Common stock reserved for issuance |  | 2,565,984 |  | 2,565,984 |  | 6,579,361
Options available for grant, options granted |  |  | 0 |  |  |
Options, weighted-average grant-date fair value |  | $ 6.09 |  | $ 3.16 | $ 1.04 |
Stock-based compensation expense |  | $ 448,000 | $ 22,000 | $ 610,000 | $ 62,000 |
Total unrecognized stock-based compensation costs related to stock options |  | $ 2,800,000 |  | $ 2,800,000 |  |
Period of unrecognized stock-based compensation costs to be recognized |  |  |  | 3 years |  |
2016 Equity Incentive Plan [Member] |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Common stock reserved for issuance | 1,200,000 | 1,200,000 |  | 1,200,000 |  |
Vesting percentage of requisite service period | 25.00% |  |  |  |  |
Additional vesting years | 3 years |  |  |  |  |
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 |  |  |  |  |
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% |  |  |  |  |
Non-employee Consultants [Member] |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Options granted |  | 7,752 | 0 | 25,647 | 0 |
Stock-based compensation expense |  | $ 226,000 | $ 4,000 | $ 264,000 | $ 14,000 |

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