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Summary of Significant Accounting Policies - Stock-Based Compensation - General Information (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]      
Expected dividend rate (as a percent) 0.00% 0.00% 0.00%