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Stock-based compensation, Stock Options (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
May 29, 2018
Oct. 27, 2016
Stock Options [Member]        
Number of Stock Options [Abstract]        
Outstanding at beginning period (in shares) 4,342,765 865,722    
Granted (in shares) 875,000 3,770,877    
Exercised (in shares) (86,250) 0    
Expired/forfeited (in shares) (223,477) (293,834)    
Outstanding at end of period (in shares) 4,908,038 4,342,765    
Exercisable at end of period (in shares) 1,904,526      
Options expected to vest at end of period (in shares) 3,003,512      
Weighted Average Exercise Price [Abstract]        
Outstanding at beginning of period (in dollars per share) $ 2.02 $ 4.74    
Granted (in dollars per share) 2.46 1.48    
Exercised (in dollars per share) 1.74 0    
Expired/forfeited (in dollars per share) 6.43 2.80    
Outstanding at end of period (in dollars per share) 1.90 $ 2.02    
Exercisable at end of period (in dollars per share) 2.04      
Options expected to vest at end of period (in dollars per share) $ 1.82      
Stock Incentive Plan 2016 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for issuance (in shares) 432,774   3,134,365 2,058,880