Quarterly report pursuant to Section 13 or 15(d)

Stock-based compensation - Narrative (Details)

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Stock-based compensation - Narrative (Details)
 1 Months Ended 3 Months Ended 6 Months Ended
Jun. 30, 2017
USD ($)
board_member
$ / shares
shares
Apr. 10, 2017
board_member
$ / shares
shares
Oct. 31, 2013
shares
Jun. 30, 2017
USD ($)
$ / shares
shares
Jun. 30, 2016
USD ($)
Jun. 30, 2017
USD ($)
$ / shares
shares
Jun. 30, 2016
USD ($)
Dec. 31, 2016
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Options outstanding (in shares) 2,160,535     2,160,535   2,160,535   1,857,012
Stock-based compensation | $           $ 544,419 $ 379,928  
Options granted, weighted-average grant date fair value (in dollars per share) | $ / shares           $ 2.13    
Number of board members granted awards | board_member 4 1            
Number of shares granted (in shares)           960,000    
Restricted Stock                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Options outstanding (in shares) 875,000     875,000   875,000   716,250
Number of shares granted (in shares)           410,000    
Stock Options                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unrecognized compensation cost related to unvested stock-based awards | $ $ 1,400,000     $ 1,400,000   $ 1,400,000    
Unrecognized compensation cost, recognition period           3 years 7 months 24 days    
Options granted, weighted-average grant date fair value (in dollars per share) | $ / shares           $ 1.37    
Stock Options | General and Administrative Expense                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation | $       391,080 $ 235,961 $ 544,419 $ 379,928  
The 2013 Plan                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Authorized shares (in shares)     4,773,992          
Contractual term     10 years          
Award vesting period     5 years          
Director                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares) 18,433 22,167            
Director | Stock Options                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation | $       $ 205,000   $ 205,000    
Share price | $ / shares $ 2.17 $ 2.03   $ 2.17   $ 2.17