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Share-Based Compensation - Assumptions Used to Determine Fair Value of Options Granted (Details) - Stock Options
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Assumptions used to determine fair value of options granted      
Dividend yield 1.60% 1.70% 0.80%
Expected volatility 30.50% 29.40% 25.50%
Risk-free interest rate 0.90% 1.50% 2.80%
Expected life of options (in years) 5 years 8 months 12 days 5 years 8 months 12 days 5 years 8 months 12 days
Forfeiture rate 0.00% 0.00% 0.00%