Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock-Based Compensation (Details)

v3.19.1
Stockholders' equity - Stock-Based Compensation (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jul. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Historical forfeiture rate (percent) 15.00%    
Warrants granted   250,000  
Warrant exercise price per share (in dollars per share)   $ 4.00 $ 4.00
Options granted, exercise price range, lower limit (usd per share) $ 2.30    
Options granted, exercise price range, upper limit (usd per share) $ 4.04    
Tecogen      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options granted 367,500 45,000  
Options granted, exercise price range, lower limit (usd per share) $ 2.30 $ 3.22  
Options granted, exercise price range, upper limit (usd per share) $ 4.04 $ 3.72  
Award vesting period 4 years    
Award expiration period 10 years    
Fair value of options issued $ 365,054 $ 41,113  
Weighted-average grant date fair value of options granted $ 0.99 $ 0.91  
Exercised, aggregate intrinsic value $ 137,085 $ 149,598  
Exercised (shares) (57,854) (156,124)  
Recognized stock-based compensation $ 181,188 $ 183,768  
Compensation cost related to unvested restricted stock awards and stock option awards not yet recognized $ 415,941 $ 281,554  
Compensation cost not yet recognized, weighted average period of recognition 2 years 6 days    
Tecogen | Restricted stock | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 25.00%    
Tecogen | Restricted stock | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 1 year    
Vesting percentage 33.00%    
Tecogen | Amended Plan | Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares of common stock reserved for future issuance 3,838,750    
Number of shares remaining available for future issuance 1,990,980 2,123,747  
Remaining Options | Tecogen | Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period   4 years  
Award expiration period   10 years