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Stockholders' Equity and Stock Plans - Valuation Assumptions (Details) - Stock options
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 2.60% 1.66%
Expected dividend yield on common stock 1.76% 1.70%
Expected life in years 5 years 10 months 24 days 2 years 4 months 24 days
Expected price volatility 22.47% 25.58%