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Summary of Significant Accounting Policies - Concentration (Details) - customer
3 Months Ended 6 Months Ended 12 Months Ended 18 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Jun. 30, 2020
Sales | Customer            
Risk and Uncertainties            
Number of customers exceeding 10% of benchmark 0 0 0 0    
Concentration risk (as a percent)           10.00%
Accounts receivable | Credit            
Risk and Uncertainties            
Number of customers exceeding 10% of benchmark     0   0  
Concentration risk (as a percent)           10.00%