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Summary Of Significant Accounting Policies - Revenue by Major Payers (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018
Revenue Benchmark | Supplier Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue |  | 97.00% | 95.00%
Medicare | Revenue Benchmark | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue |  | 25.00% | 30.00%
Medicare | Accounts Receivable | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue | 26.00% |  |
Blue Shield | Revenue Benchmark | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue |  | 12.00% | 14.00%
Blue Shield | Accounts Receivable | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue | 16.00% | 15.00% |
United Healthcare | Revenue Benchmark | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue |  | 11.00% | 12.00%
United Healthcare | Accounts Receivable | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue | 11.00% | 22.00% |
Medicare Advantage | Revenue Benchmark | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue |  | 11.00% | 10.00%
Medicare Advantage | Accounts Receivable | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue | 11.00% |  |
Janssen (SIMPONI) | Accounts Receivable | Customer Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue |  | 19.00% |
AVISE CTD Test | Revenue Benchmark | Product Concentration Risk |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Percent of total revenue |  | 82.00% | 82.00%

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