Employee Stock Purchase Plan and Stock-Based Compensation - Summary of Option Activity (Details) - 2004 Plan and 2018 Equity Incentive Plan - USD ($)
$ / shares in Units, $ in Thousands |
9 Months Ended |
12 Months Ended |
Sep. 30, 2018 |
Dec. 31, 2017 |
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
|
|
| Shares Available for Grant, Beginning Balance |
91,149
|
|
| Shares Available for Grant, Increase in authorized shares |
5,053,013
|
|
| Shares Available for Grant, Granted |
(2,570,848)
|
|
| Shares Available for Grant, Exercised |
0
|
|
| Shares Available for Grant, Canceled |
3,721
|
|
| Shares Available for Grant, Ending Balance |
2,577,035
|
91,149
|
| Outstanding Options, Beginning Balance |
835,320
|
|
| Options granted to purchase common stock |
2,570,848
|
|
| Outstanding Options Exercised |
(19,691)
|
|
| Outstanding Options Canceled |
(3,721)
|
|
| Outstanding Options, Ending Balance |
3,382,756
|
835,320
|
| Outstanding Options Exercisable |
650,197
|
|
| Outstanding Options Vested and expected to vest |
3,172,528
|
|
| Weighted - Average Exercise Price, Beginning Balance |
$ 10.31
|
|
| Weighted - Average Exercise Price, Granted |
13.15
|
|
| Weighted - Average Exercise Price, Exercised |
6.67
|
|
| Weighted - Average Exercise Price, Canceled |
13.58
|
|
| Weighted - Average Exercise Price, Ending Balance |
0
|
$ 10.31
|
| Weighted - Average Exercise Price, Exercisable |
0
|
|
| Weighted - Average Exercise Price, Vested and expected to vest |
$ 0
|
|
| Weighted - Average Remaining Contract Term |
8 years 5 months 4 days
|
6 years 10 months 2 days
|
| Weighted - Average Remaining Contract Term, Exercisable |
5 years 9 months 18 days
|
|
| Weighted - Average Remaining Contract Term, Vested and expected to vest |
8 years 4 months 20 days
|
|
| Aggregate Intrinsic Value, Balance |
$ 8,434
|
$ 3,813
|
| Aggregate Intrinsic Value, Exercisable |
3,486
|
|
| Aggregate Intrinsic Value, Vested and expected to vest |
$ 8,073
|
|