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Summary of Significant Accounting Policies - Stock-based Compensation (Details)
12 Months Ended
Dec. 31, 2019
Restricted stock units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock options vesting period (in years) 4 years
2012 Employee Stock Purchase Plan  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Award offering period 6 months