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Summary of Significant Accounting Policies - Concentration of Credit Risk (Details) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Minimum |  |  |
Concentration Risk [Line Items] |  |  |
Customer contracts, term of contracts | 3 years |  |
Maximum |  |  |
Concentration Risk [Line Items] |  |  |
Customer contracts, term of contracts | 5 years |  |
Top Five Customers | Customer Concentration Risk | Revenue |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 68.00% | 69.20% | 69.00%

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