Commitments and contingencies Commitments and contingencies - Prior period schedule of future minimum lease payments (Details) (Details) $ in Thousands |
12 Months Ended |
|---|---|
|
Dec. 31, 2018
USD ($)
| |
| Leases [Abstract] | |
| 2019 | $ 1,637 |
| 2020 | 274 |
| Total | 1,911 |
| Prior year rent expense | $ 1,500 |