Income taxes (Details) - USD ($)
$ in Thousands |
12 Months Ended |
Dec. 31, 2019 |
Dec. 31, 2018 |
| Deferred tax assets: |
|
|
| U.S. and state net operating loss carryforwards |
$ 56,906
|
$ 49,614
|
| Capitalized R&D |
28,427
|
25,366
|
| Research and development credits |
11,717
|
10,445
|
| Lease liability |
1,779
|
0
|
| Stock-based compensation |
1,053
|
1,989
|
| Depreciation and amortization |
545
|
640
|
| Accrued expenses |
507
|
450
|
| Other temporary differences |
38
|
85
|
| Total deferred tax assets |
100,972
|
88,589
|
| Less valuation allowance |
(99,249)
|
(88,589)
|
| Deferred tax assets less valuation allowance |
1,723
|
0
|
| ROU asset |
(1,723)
|
0
|
| Total deferred tax liabilities |
(1,723)
|
0
|
| Net deferred tax assets (deferred tax liabilities) |
$ 0
|
$ 0
|
| Reconciliation of income tax expense |
|
|
| Federal income tax expense at statutory rate |
21.00%
|
21.00%
|
| State income tax, net of federal benefit |
6.30%
|
8.90%
|
| Permanent differences |
0.00%
|
9.00%
|
| Research and development credit |
3.30%
|
6.70%
|
| Change in valuation allowance |
(27.40%)
|
(43.10%)
|
| Other, net |
(3.20%)
|
(2.50%)
|
| Effective tax rate |
0.00%
|
0.00%
|