Quarterly report pursuant to Section 13 or 15(d)

Stock Plans - Fair value of stock options (Details)

v3.20.2
Stock Plans - Fair value of stock options (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Stock Plans        
Weighted-average risk-free interest rate 0.40% 2.10% 0.40% 2.20%
Expected dividend payments $ 0 $ 0 $ 0 $ 0
Expected holding period (years) 5 years 9 months 18 days 5 years 10 months 24 days 5 years 9 months 18 days 5 years 4 months 24 days
Weighted-average volatility factor 1.04% 0.93% 1.04% 0.94%
Estimated forfeiture rates for options granted 28.00% 21.00% 28.00% 21.00%