Annual report pursuant to Section 13 and 15(d)

Stock Plans - Fair value of stock options (Details)

v3.21.1
Stock Plans - Fair value of stock options (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Stock Plans    
Weighted-average risk-free interest rate 0.40% 2.21%
Expected dividend payments $ 0 $ 0
Expected holding period (years) 5 years 9 months 15 days 5 years 4 months 28 days
Weighted-average volatility factor 1.04% 0.94%
Estimated forfeiture rates for options granted 27.00% 21.00%