Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock Option Activity (Details)

v3.20.1
Stockholders' equity - Stock Option Activity (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Exercise Price Per Share [Abstract]    
Granted, Exercise Price Lower Range Limit (usd per share) $ 3.40  
Granted, Exercise Price Upper Range Limit (usd per share) $ 3.80  
Tecogen    
Stock Options Outstanding [Roll Forward]    
Beginning (shares) 1,292,589  
Granted (shares) 88,500 367,500
Exercised (shares) (24,515) (57,854)
Canceled and forfeited (shares) (3,700)  
Ending (shares) 1,352,874 1,292,589
Exercisable (shares) 953,499  
Vested and expected to vest (shares) 1,292,968  
Weighted Average Exercise Price [Roll Forward]    
Beginning (usd per share) $ 3.52  
Granted (usd per share) 3.70  
Exercised (usd per share) 1.37  
Canceled and forfeited (usd per share) 3.46  
Ending (usd per share) $ 3.57 $ 3.52
Exercised, aggregate intrinsic value $ 19,794 $ 137,085
Exercisable (usd per share) $ 3.54  
Vested and expected to vest (usd per share) $ 3.57  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]    
Outstanding, Aggregate Intrinsic Value $ 95,381 $ 671,331
Exercisable, Aggregate Intrinsic Value 95,381  
Vested and expected to vest, Aggregate Intrinsic Value $ 95,381  
Exercise Price Per Share [Abstract]    
Outstanding, Exercise Price Lower Range Limit (usd per share) $ 0.79 $ 0.79
Outstanding, Exercise Price Upper Range Limit (usd per share) 10.33 10.33
Granted, Exercise Price Lower Range Limit (usd per share) 3.40 2.30
Granted, Exercise Price Upper Range Limit (usd per share) 3.80 $ 4.04
Exercised, Exercise Price Range, Lower Range Limit (usd per share) 1.20  
Exercised, Exercise Price Range, Upper Range Limit (usd per share) 2.60  
Canceled and Forfeited, Exercise Price Lower Range Limit (usd per share) 3.22  
Canceled and Forfeited, Exercise Price Upper Range Limit (usd per share) $ 4.50  
Stock Options | Tecogen    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]    
Outstanding, Weighted Average Remaining Life 5 years 3 months 20 days 5 years 11 months 5 days