Quarterly report pursuant to Section 13 or 15(d)

Fair value measurements (Schedule of Changes in Level 3 Liabilities Measured at Fair Value) (Details)

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Fair value measurements (Schedule of Changes in Level 3 Liabilities Measured at Fair Value) (Details) - USD ($)
3 Months Ended 6 Months Ended 9 Months Ended
Mar. 31, 2019
Sep. 30, 2019
Sep. 30, 2019
Sep. 30, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Conversion of convertible notes to common stock     $ (10,225,959)  
Reclassification of warrant liability to equity     5,438,660
Convertible Notes [Member] | Fair Value, Inputs, Level 3 [Member]        
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Issuance of senior secured convertible notes $ 6,330,726      
Issuance of warrants in connection with convertible notes      
Balance Beginning 6,330,726 $ 7,975,308 6,330,726  
Change in fair value 1,644,582 2,250,651    
Conversion of convertible notes to common stock   (10,225,959)    
Reclassification of warrant liability to equity      
Balance Ending 7,975,308  
Warrant [Member] | Fair Value, Inputs, Level 3 [Member]        
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Issuance of senior secured convertible notes      
Issuance of warrants in connection with convertible notes 2,568,934      
Balance Beginning 2,568,934 5,322,162 2,568,934  
Change in fair value 2,753,228 116,498    
Conversion of convertible notes to common stock      
Reclassification of warrant liability to equity   (5,438,660)    
Balance Ending $ 5,322,162