Annual report pursuant to Section 13 and 15(d)

Convertible debentures and loan due to related party (Details)

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Convertible debentures and loan due to related party (Details) - USD ($)
3 Months Ended 12 Months Ended
Dec. 14, 2017
Dec. 23, 2013
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Feb. 26, 2018
Sep. 30, 2017
Apr. 01, 2016
Mar. 31, 2016
Debt Instrument [Line Items]                  
Payment made to terminate senior convertible promissory note       $ 3,150,000 $ 0        
Michaelson                  
Debt Instrument [Line Items]                  
Related party ownership percentage       5.00%          
Convertible debentures | Michaelson                  
Debt Instrument [Line Items]                  
Payment made to terminate senior convertible promissory note $ 3,150,000                
Principal amount   $ 3,000,000           $ 3,150,000  
Related party debt, stated interest rate     4.00%            
Debt term   3 years              
Conversion price in usd per share               $ 3.54 $ 3.37
Percentage of principal and interest     120.00%            
Chief Executive Officer (John N. Hatsopoulos)                  
Debt Instrument [Line Items]                  
Loan from related party     $ 850,000 $ 850,000     $ 850,000    
Demand notes | Chief Executive Officer (John N. Hatsopoulos)                  
Debt Instrument [Line Items]                  
Stated interest rate (percent)     6.00% 6.00%     6.00%    
Subsequent Event | Summary of Proposed Terms and Conditions | Revolving credit facility                  
Debt Instrument [Line Items]                  
Credit facility, maximum borrowing capacity           $ 10,000,000