Quarterly financial information (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands |
3 Months Ended | 12 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2019 |
Sep. 30, 2019 |
Jun. 30, 2019 |
Mar. 31, 2019 |
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Quarterly Financial Information Disclosure [Abstract] | ||||||||||
| Operating expenses | $ 9,862 | $ 9,584 | $ 10,066 | $ 9,477 | $ 8,886 | $ 10,460 | $ 9,788 | $ 10,384 | $ 38,989 | $ 39,518 |
| Net income (loss) | $ (9,356) | $ (7,532) | $ (6,495) | $ (15,567) | $ 350 | $ (7,833) | $ (4,438) | $ (15,890) | $ (38,950) | $ (27,811) |
| Net loss per share - basic and diluted (in USD per share) | $ (0.34) | $ (0.28) | $ (0.42) | $ (1.22) | $ 0.03 | $ (0.72) | $ (0.42) | $ (1.78) | $ (1.89) | $ (2.69) |
| Weighted-average number of common shares used in net loss per share - basic and diluted (in shares) | 27,620 | 26,681 | 15,344 | 12,713 | 10,847 | 10,829 | 10,693 | 8,905 | 20,644 | 10,321 |