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Summary of Significant Accounting Policies - Concentration of Credit Risk (Details) - Institution
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Concentration Risk [Line Items]      
Number of financial institutions where substantially all of the cash is maintained 1    
Accounts Receivable | Credit Concentration Risk      
Concentration Risk [Line Items]      
Concentration risk (as a percent) 28.00% 31.00% 48.00%
Accounts Receivable | Credit Concentration Risk | Largest customer      
Concentration Risk [Line Items]      
Concentration risk (as a percent) 14.00% 17.00% 25.00%
Accounts Receivable | Credit Concentration Risk | Second largest customer      
Concentration Risk [Line Items]      
Concentration risk (as a percent) 17.00% 14.00% 13.00%
Accounts Receivable | Credit Concentration Risk | Third largest customer      
Concentration Risk [Line Items]      
Concentration risk (as a percent)     10.00%