Property and equipment (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Property and equipment    
Less accumulated depreciation $ (1,123) $ (590)
Property and equipment, net 1,690 1,816
Depreciation and amortization 457 405
Computer software and equipment    
Property and equipment    
Property and equipment, gross 15 15
Office equipment and furniture    
Property and equipment    
Property and equipment, gross 176 92
Laboratory equipment    
Property and equipment    
Property and equipment, gross 1,571 1,529
Leasehold improvements    
Property and equipment    
Property and equipment, gross $ 1,051 748
Construction in progress    
Property and equipment    
Property and equipment, gross   $ 22