Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock-Based Compensation (Details)

v3.8.0.1
Stockholders' equity - Stock-Based Compensation (Details) - USD ($)
1 Months Ended 12 Months Ended
Jul. 31, 2016
Jul. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Historical forfeiture rate (percent)       15.00%  
Warrants granted     900,000   250,000
Warrant exercise price per share (in dollars per share) $ 4.00 $ 4.00     $ 4.00
Warrants exercised for investment in joint venture   $ 2,700,000.0      
Warrants expired (shares) 225,000        
Options granted, exercise price range, lower limit (usd per share)       $ 3.22  
Options granted, exercise price range, upper limit (usd per share)       $ 3.72  
Warrant          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Warrants exercised (shares)   675,000      
Tecogen          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Options granted       45,000 207,701
Options granted, exercise price range, lower limit (usd per share)       $ 3.22 $ 0.79
Options granted, exercise price range, upper limit (usd per share)       $ 3.72 $ 4.27
Award vesting period       4 years  
Award expiration period       10 years  
Fair value of options issued       $ 41,113 $ 236,315
Weighted-average grant date fair value of options granted       $ 0.91 $ 1.14
Recognized stock-based compensation       $ 183,768 $ 165,931
Compensation cost related to unvested restricted stock awards and stock option awards not yet recognized       $ 281,554 $ 444,939
Compensation cost not yet recognized, weighted average period of recognition       1 year 6 months 26 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       2,123,747 1,607,357
Options Issued in Conjunction with Ilios Merger | Tecogen          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Options granted         82,701
Remaining Options | Tecogen          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Options granted         125,000
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