Stock Incentive Plans - Additional Information (Detail) - USD ($)
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1 Months Ended |
6 Months Ended |
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Mar. 31, 2018 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
Jul. 31, 2017 |
Feb. 28, 2017 |
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Total intrinsic value of options exercised |
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$ 1,000,000
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| Weighted-average grant date fair value per share for options granted |
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$ 8.38
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$ 0.33
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| Remaining shares subject to repurchase |
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219,747
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265,098
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| Liability for unvested common shares subject to repurchase included in accrued expenses and other liabilities |
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$ 116,801
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$ 122,551
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| 2015 Stock Incentive Plan |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Number of shares available for issuance |
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3,225,346
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2,446,323
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| Stock option vesting period |
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4 years
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| Stock options expiration period |
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10 years
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| Number of additional available for future grant |
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0
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| 2018 Incentive Award Plan |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Number of shares available for issuance |
3,186,205
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| Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock |
4.00%
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| Maximum shares of common stock may be issued |
20,887,347
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| Number of shares outstanding available for future grant |
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2,493,415
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| 2018 Employee Stock Purchase Plan |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Number of shares available for issuance |
353,980
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| Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock |
1.00%
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| Maximum shares allowed to be issued under ESPP |
4,778,738
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| 2015 and 2018 Stock Incentive Plans |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Unrecognized compensation expense |
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$ 9,300,000
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| Unrecognized compensation expense estimated to be recognized over period |
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3 years 4 months 24 days
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