Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Weighted Average Assumptions (Details)

v3.6.0.2
Stockholders' equity - Weighted Average Assumptions (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Historical forfeiture rate 15.00%  
Tecogen    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Compensation cost not yet recognized, weighted average period of recognition 2 years 11 months 5 days  
Tecogen | Stock Options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life 6 years 3 months 6 years 3 months
Risk-free interest rate, Minimum 1.18% 1.63%
Risk-free interest rate, Maximum 1.90% 1.67%
Expected volatility, Minimum 27.20% 32.40%
Expected volatility, Maximum 32.80% 32.60%