Quarterly report pursuant to Section 13 or 15(d)

Basis of presentation, principles of consolidation and significant accounting policies - Narrative (Details)

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Basis of presentation, principles of consolidation and significant accounting policies - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Class of Warrant or Right [Line Items]          
Accumulated deficit $ 21,532   $ 21,532   $ 14,480
Warrant          
Class of Warrant or Right [Line Items]          
Anti-dilutive securities (in shares) 3,784,515 948,011 3,784,515 948,011  
Employee Stock Option          
Class of Warrant or Right [Line Items]          
Anti-dilutive securities (in shares) 2,754,000 530,000 2,754,000 530,000