Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock-Based Compensation (Details)

v3.20.1
Stockholders' equity - Stock-Based Compensation (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Historical forfeiture rate (percent) 15.00%  
Options granted, exercise price range, lower limit (usd per share) $ 3.40  
Options granted, exercise price range, upper limit (usd per share) $ 3.80  
Tecogen    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options granted 88,500 367,500
Options granted, exercise price range, lower limit (usd per share) $ 3.40 $ 2.30
Options granted, exercise price range, upper limit (usd per share) $ 3.80 $ 4.04
Award vesting period 4 years  
Award expiration period 10 years  
Fair value of options issued $ 89,772 $ 365,054
Weighted-average grant date fair value of options granted $ 1.01 $ 0.99
Exercised, aggregate intrinsic value $ 19,794 $ 137,085
Exercised (shares) 24,515 57,854
Recognized stock-based compensation $ 163,464 $ 181,188
Compensation cost related to unvested restricted stock awards and stock option awards not yet recognized $ 340,503 $ 415,941
Compensation cost not yet recognized, weighted average period of recognition 1 year 8 months 1 day  
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 1,906,180 1,990,980
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