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Stock Plans and Share-Based Compensation - Weighted Average Assumptions Used for Performance Units (Details) - Performance Units
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Weighted-Average Assumptions Used:    
Risk-free Interest Rate 0.20% 1.40%
Annualized Volatility 33.60% 24.50%
Expected Life (in years) 2 years 10 months 24 days 2 years 10 months 24 days