Revenue - Schedule of Concentration of Risk, by Risk Factor (Details) - Third-Party Payor Concentration Risk	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Medicare \| Percentage of Revenues
Disaggregation of Revenue [Line Items]
Concentration risk percentage	44.00%	47.00%	49.00%
Medicare \| Percentage of Accounts Receivable (current)
Disaggregation of Revenue [Line Items]
Concentration risk percentage	18.00%	18.00%
Payor A \| Percentage of Revenues
Disaggregation of Revenue [Line Items]
Concentration risk percentage	16.00%	15.00%	14.00%
Payor A \| Percentage of Accounts Receivable (current)
Disaggregation of Revenue [Line Items]
Concentration risk percentage	15.00%	19.00%
Payor A \| Percentage of Accounts Receivable (noncurrent)
Disaggregation of Revenue [Line Items]
Concentration risk percentage	16.00%	15.00%
Payor B \| Percentage of Accounts Receivable (current)
Disaggregation of Revenue [Line Items]
Concentration risk percentage	22.00%	20.00%
Payor B \| Percentage of Accounts Receivable (noncurrent)
Disaggregation of Revenue [Line Items]
Concentration risk percentage	10.00%	12.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

CASTLE BIOSCIENCES INC 10-K