Related parties (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Series D Preferred Stock        
Related parties        
Preferred shares issued       50,670
Proceeds from common stock issued       $ 7.4
Common stock        
Related parties        
Shares issued       1,303,750
Proceeds from shares issued       $ 18.3
University of Basel        
Related parties        
Research and development expenses $ 0.0   $ 0.3 0.3
Royalties paid $ 0.0 $ 0.0 $ 0.0 $ 0.0
University of Basel | Maximum        
Related parties        
Research and development expenses   $ 0.1