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Employee Stock Purchase Plan, Stock Options and Warrants - Option Granted Fair Value Calculation Assumptions (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]      
Risk-free interest rate, minimum 0.29% 1.38% 2.63%
Risk-free interest rate, maximum 1.67% 2.56% 2.77%
Expected option term / Performance Period     5 years
Expected price volatility, minimum 38.65% 28.66% 34.06%
Expected price volatility, maximum 45.12% 39.38% 34.32%
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected option term / Performance Period 4 years 3 years  
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected option term / Performance Period 5 years 5 years