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Employee Benefits and Share-Based Compensation - Assumptions Used to Value Stock Options Granted (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]      
Expected life 4 years 8 months 12 days 4 years 4 months 24 days 4 years 9 months 18 days
Expected volatility 39.40% 33.70% 31.10%
Risk-free interest rate 0.70% 2.00% 2.80%
Estimated forfeiture rate 5.70% 7.20% 6.90%
Dividend yield 0.00% 0.00% 0.00%