Quarterly report pursuant to Section 13 or 15(d)

Stock Plans - Fair value of stock options (Details)

v3.21.2
Stock Plans - Fair value of stock options (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Stock Plans        
Weighted-average risk-free interest rate 0.00% 0.40% 0.50% 0.40%
Expected dividend payments $ 0 $ 0 $ 0 $ 0
Expected holding period (years) 0 years 5 years 9 months 18 days 5 years 6 months 5 years 9 months 18 days
Weighted-average volatility factor 0.00% 1.04% 1.14% 1.04%
Estimated forfeiture rates for options granted 0.00% 28.00% 30.00% 28.00%