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Stock-Based Compensation - Assumptions Used to Calculate Fair Value (Details) - Performance RSUs
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate, minimum 0.10% 1.58% 2.48%
Risk-free interest rate, maximum 0.13% 1.59% 2.63%
Expected term (years) 3 years 3 years 3 years
Expected share price volatility, minimum (percent) 30.16% 12.89% 14.76%
Expected share price volatility, maximum (percent) 40.95% 15.51% 17.71%