Investments and Fair Value of Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands |
12 Months Ended |
Dec. 31, 2018 |
Dec. 31, 2017 |
| Marketable securities |
|
|
| Amortized Cost |
$ 97,016
|
|
| Gross Unrealized Losses |
(29)
|
|
| Fair Value |
96,987
|
|
| Assets: |
|
|
| Investments |
96,987
|
|
| Transfers between Level 1, Level 2 or Level 3 |
|
|
| Transfer from Level 1 to Level 2, assets |
0
|
$ 0
|
| Transfer from Level 2 to Level 1, assets |
0
|
0
|
| Transfers into Level 3, assets |
0
|
0
|
| Transfer out of Level 3, assets |
0
|
0
|
| Transfer from Level 1 to Level 2, liabilities |
0
|
0
|
| Transfer from Level 2 to Level 1, liabilities |
0
|
0
|
| Transfers into Level 3, liabilities |
0
|
|
| U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Amortized Cost |
17,704
|
|
| Gross Unrealized Losses |
(3)
|
|
| Fair Value |
17,701
|
|
| Assets: |
|
|
| Investments |
17,701
|
|
| U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Amortized Cost |
79,312
|
|
| Gross Unrealized Losses |
(26)
|
|
| Fair Value |
79,286
|
|
| Assets: |
|
|
| Investments |
79,286
|
|
| Preferred stock warrant liability |
|
|
| Roll forward of aggregate fair values of preferred stock warrants |
|
|
| Fair value at beginning of period |
866
|
67
|
| Issuance of warrants to purchase shares of Series B convertible preferred stock |
|
14
|
| Change in fair value through the exercise date |
2,187
|
785
|
| Reclassification to additional paid-in capital in connection with IPO |
(3,053)
|
|
| Fair value at end of period |
|
866
|
| Recurring |
|
|
| Assets: |
|
|
| Assets |
404,051
|
|
| Recurring | Money market funds |
|
|
| Assets: |
|
|
| Cash equivalents |
282,160
|
104,288
|
| Recurring | U.S. treasury bills |
|
|
| Assets: |
|
|
| Cash equivalents |
24,904
|
|
| Recurring | U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Fair Value |
17,701
|
|
| Assets: |
|
|
| Investments |
17,701
|
|
| Recurring | U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Fair Value |
79,286
|
|
| Assets: |
|
|
| Investments |
79,286
|
|
| Recurring | Preferred stock warrant liability |
|
|
| Liabilities: |
|
|
| Liabilities |
|
866
|
| Recurring | Level 1 |
|
|
| Assets: |
|
|
| Assets |
282,160
|
|
| Recurring | Level 1 | Money market funds |
|
|
| Assets: |
|
|
| Cash equivalents |
282,160
|
104,288
|
| Recurring | Level 2 |
|
|
| Assets: |
|
|
| Assets |
121,891
|
|
| Recurring | Level 2 | U.S. treasury bills |
|
|
| Assets: |
|
|
| Cash equivalents |
24,904
|
|
| Recurring | Level 2 | U.S. government agency bonds |
|
|
| Marketable securities |
|
|
| Fair Value |
17,701
|
|
| Assets: |
|
|
| Investments |
17,701
|
|
| Recurring | Level 2 | U.S. treasury notes |
|
|
| Marketable securities |
|
|
| Fair Value |
79,286
|
|
| Assets: |
|
|
| Investments |
$ 79,286
|
|
| Recurring | Level 3 | Preferred stock warrant liability |
|
|
| Liabilities: |
|
|
| Liabilities |
|
$ 866
|