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Commitments and contingencies - Summary of Significant Contractual Obligations and Commercial Commitments (Details) - USD ($)
Dec. 31, 2018
May 31, 2018
Jul. 31, 2017
Operating Leased Assets [Line Items]      
Total $ 338,414    
Less than 1 year 122,858    
Office Space Located in Maynard, Massachusetts      
Operating Leased Assets [Line Items]      
Total 278,000   $ 332,824
Less than 1 year 63,000    
1-3 years 131,000    
3-5 years 84,000    
More than 5 years 0    
Panama Farm Site      
Operating Leased Assets [Line Items]      
Total 60,000 $ 180,000  
Less than 1 year 60,000    
1-3 years 0    
3-5 years 0    
More than 5 years 0    
Indiana auto lease [Member]      
Operating Leased Assets [Line Items]      
Total 11,000    
Less than 1 year 5,000    
1-3 years 6,000    
3-5 years 0    
More than 5 years 0    
Indiana well lease [Member]      
Operating Leased Assets [Line Items]      
Total 717,000    
Less than 1 year 15,000    
1-3 years 32,000    
3-5 years 33,000    
More than 5 years 637,000    
Significant Contractual Obligations and Commercial Commitments [Member]      
Operating Leased Assets [Line Items]      
Total 1,066,000    
Less than 1 year 143,000    
1-3 years 169,000    
3-5 years 117,000    
More than 5 years $ 637,000