Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock Option Activity (Details)

v3.8.0.1
Stockholders' equity - Stock Option Activity (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Exercise Price Per Share [Abstract]    
Granted, Exercise Price Lower Range Limit (usd per share) $ 3.22  
Granted, Exercise Price Upper Range Limit (usd per share) 3.72  
Assumed in merger Exercise Price Lower Range Limit (usd per share) 3.15  
Assumed in merger, Exercise Price Upper Range Limit (usd per share) $ 30.33  
Tecogen    
Stock Options Outstanding [Roll Forward]    
Beginning (shares) 1,117,918  
Granted (shares) 45,000 207,701
Assumed in merger (shares) 156,124  
Exercised (shares) (122,043)  
Canceled and forfeited (shares) (135,447)  
Ending (shares) 1,061,552 1,117,918
Exercisable (shares) 874,202  
Vested and expected to vest (shares) 1,033,450  
Weighted Average Exercise Price [Roll Forward]    
Beginning (usd per share) $ 3.10  
Granted (usd per share) 3.35  
Assumed in merger (usd per share) 10.35  
Exercised (usd per share) 1.47  
Canceled and forfeited (usd per share) 9.28  
Ending (usd per share) 3.60 $ 3.10
Exercisable (usd per share) 3.46  
Vested and expected to vest (usd per share) $ 3.58  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]    
Outstanding, Aggregate Intrinsic Value $ 291,449 $ 1,415,150
Exercisable, Aggregate Intrinsic Value 291,449  
Vested and expected to vest, Aggregate Intrinsic Value $ 291,449  
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) 5.39 5.39
Granted, Exercise Price Lower Range Limit (usd per share) 3.22 0.79
Granted, Exercise Price Upper Range Limit (usd per share) 3.72 $ 4.27
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) 3.39  
Canceled and Forfeited, Exercise Price Upper Range Limit (usd per share) $ 4.96  
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 4 years 11 months 12 days 5 years