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Basis of presentation, principles of consolidation and significant accounting policies - Fair Value of Warrant Liability (Details) - Recurring - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Fair value of derivative liability $ 6,820 $ 1,508
Quoted Pricesin ActiveMarkets forIdenticalAssets (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Fair value of derivative liability 0 0
Significant OtherObservable Inputs(Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Fair value of derivative liability 0 0
Significant OtherUnobservable Inputs(Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis    
Fair value of derivative liability $ 6,820 $ 1,508