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Stockholders' Equity and Stock Plans - Valuation Assumptions (Details) - Stock options
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 0.91% 2.51% 2.60%
Expected dividend yield on common stock 2.38% 1.75% 1.76%
Expected life in years 6 years 1 month 6 days 5 years 9 months 18 days 5 years 10 months 24 days
Expected price volatility 24.43% 22.71% 22.47%