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Employee Benefits and Share-Based Compensation - Assumptions Used to Value Stock Options Granted (Details) - Stock Options
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life 4 years 10 months 24 days 4 years 8 months 12 days
Expected volatility, % 30.10% 33.60%
Risk-free interest rate, % 0.60% 1.40%
Estimated forfeiture rate, % 7.90% 5.70%
Dividend yield, % 0.00% 0.00%