Commitments and contingencies Commitments and contingencies - Supplemental Balance Sheet (Details) - USD ($) $ in Thousands |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Lease Assets [Abstract] | ||
| Operating lease, right-of-use asset | $ 6,156 | |
| Finance Lease, Right-of-Use Asset | 150 | |
| Finance and Operating Lease, Right-of-Use Asset | 6,306 | $ 0 |
| Lease Liabilities, Current [Abstract] | ||
| Operating Lease, Liability, Current | 990 | |
| Finance Lease, Liability, Current | 127 | |
| Lease Liabilities, Noncurrent [Abstract] | ||
| Operating Lease, Liability, Noncurrent | 5,373 | |
| Finance Lease, Liability, Noncurrent | 22 | |
| Total | $ 6,512 |