| Cover | 12 Months Ended |
| Dec. 31, 2022 | |
| Document Information [Line Items] | |
| Document Type | DEF 14A |
| Amendment Flag | false |
| Entity Information [Line Items] | |
| Entity Registrant Name | CASTLE BIOSCIENCES, INC. |
| Entity Central Index Key | 0001447362 |
| Pay vs Performance Disclosure Unit_pure in Thousands | 12 Months Ended | ||
| Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | |
| Pay vs Performance Disclosure [Table] | |||
| Pay vs Performance [Table Text Block] | Pay Versus Performance We are required by SEC rules to disclose certain information regarding compensation paid to our NEOs. The amounts set forth below under the headings “Compensation Actually Paid to PEO” and “Average Compensation Actually Paid to Non-PEO S-K. Value of Initial Fixed $100 Year (a) Summary (1) (b) Compensation (2) (c) Average Non-PEO (1) (d) Average Non-PEO (2) (e) Total (3) (f) Peer Group (3) (g) Net Loss (4) (in thousands) Total (5) (in thousands) 2022 $ 7,552,577 $ 3,081,353 $ 2,670,395 $ 990,266 $ 68 $ 113 $ (67,138 ) $ 137,039 2021 $ 6,521,857 $ 2,127,860 $ 2,813,079 $ 1,240,785 $ 125 $ 125 $ (31,292 ) $ 94,085 2020 $ 5,344,639 $ 13,311,700 $ 1,953,619 $ 4,526,526 $ 195 $ 125 $ (10,284 ) $ 62,649 (1) Mr. Maetzold was our PEO for each of 2020, 2021 and 2022. In this disclosure, we refer to our NEOs other than Mr. Maetzold in any fiscal year as our “Other NEOs” or our “Non-PEO S-K, (2) For each year, in determining both the compensation actually (“CAP”) for our PEO and the average CAP for our Other NEOs, we deducted or added back the following amounts from or to the total amounts of compensation reported in column (b) and column (d) for such year. Mr. Maetzold’s CAP is calculated as follows: Year Total Stock Awards Option Change in Fair Change in Fair Year-End Fair Compensation 2022 $ 7,552,577 $ (6,102,902 ) $ — $ (1,590,589 ) $ (3,085,629 ) $ 6,307,896 $ 3,081,353 2021 $ 6,521,857 $ (2,500,003 ) $ (2,656,954 ) $ (535,559 ) $ (4,200,151 ) $ 5,498,670 $ 2,127,860 2020 $ 5,344,639 $ (1,268,982 ) $ (3,056,657 ) $ 1,060,493 $ 6,181,735 $ 5,050,472 $ 13,311,700 Other NEOs average CAP are as follows: Year Total Stock Awards Option Change in Fair Change in Fair Year-End Fair Average 2022 $ 2,670,395 $ (1,865,475 ) $ — $ (549,674 ) $ (1,212,570 ) $ 1,947,590 $ 990,266 2021 $ 2,813,079 $ (999,993 ) $ (1,062,350 ) $ (215,497 ) $ (1,493,903 ) $ 2,199,449 $ 1,240,785 2020 $ 1,953,619 $ (414,120 ) $ (947,196 ) $ 332,321 $ 2,012,760 $ 1,589,142 $ 4,526,526 (3) For each fiscal year disclosed the cumulative total shareholder return and peer group cumulative total shareholder return is calculated in the same manner as Item 201(e) of Regulation S-K (4) The dollar amounts presented are from our consolidated financial statements appearing in our Annual Report on Form 10-K (5) This is our Company-Selected Measure provided in accordance in with Item 402(v)(2)(vi) of Regulation S-K. 10-K | ||
| Company Selected Measure Name | TotalRevenue | ||
| Named Executive Officers, Footnote [Text Block] | In this disclosure, we refer to our NEOs other than Mr. Maetzold in any fiscal year as our “Other NEOs” or our “Non-PEO | ||
| Peer Group Issuers, Footnote [Text Block] | For each fiscal year disclosed the cumulative total shareholder return and peer group cumulative total shareholder return is calculated in the same manner as Item 201(e) of Regulation S-K | ||
| PEO Total Compensation Amount | $ 7,552,577 | $ 6,521,857 | $ 5,344,639 |
| PEO Actually Paid Compensation Amount | $ 3,081,353 | 2,127,860 | 13,311,700 |
| Adjustment To PEO Compensation, Footnote [Text Block] | (2) For each year, in determining both the compensation actually (“CAP”) for our PEO and the average CAP for our Other NEOs, we deducted or added back the following amounts from or to the total amounts of compensation reported in column (b) and column (d) for such year. Mr. Maetzold’s CAP is calculated as follows: Year Total Stock Awards Option Change in Fair Change in Fair Year-End Fair Compensation 2022 $ 7,552,577 $ (6,102,902 ) $ — $ (1,590,589 ) $ (3,085,629 ) $ 6,307,896 $ 3,081,353 2021 $ 6,521,857 $ (2,500,003 ) $ (2,656,954 ) $ (535,559 ) $ (4,200,151 ) $ 5,498,670 $ 2,127,860 2020 $ 5,344,639 $ (1,268,982 ) $ (3,056,657 ) $ 1,060,493 $ 6,181,735 $ 5,050,472 $ 13,311,700 | ||
| Non-PEO NEO Average Total Compensation Amount | $ 2,670,395 | 2,813,079 | 1,953,619 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 990,266 | 1,240,785 | 4,526,526 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | Other NEOs average CAP are as follows: Year Total Stock Awards Option Change in Fair Change in Fair Year-End Fair Average 2022 $ 2,670,395 $ (1,865,475 ) $ — $ (549,674 ) $ (1,212,570 ) $ 1,947,590 $ 990,266 2021 $ 2,813,079 $ (999,993 ) $ (1,062,350 ) $ (215,497 ) $ (1,493,903 ) $ 2,199,449 $ 1,240,785 2020 $ 1,953,619 $ (414,120 ) $ (947,196 ) $ 332,321 $ 2,012,760 $ 1,589,142 $ 4,526,526 | ||
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | The following chart shows the relationships between (a) the compensation actually paid to the PEO, (b) the average compensation actually paid to the Non-PEO | ||
| Compensation Actually Paid vs. Net Income [Text Block] | The following chart shows the relationships between (a) the compensation actually paid to the PEO, (b) the average compensation actually paid to the Non-PEO | ||
| Compensation Actually Paid vs. Company Selected Measure [Text Block] | The following chart shows the relationships between (a) the compensation actually paid to the PEO, (b) the average compensation actually paid to the Non-PEO | ||
| Total Shareholder Return Vs Peer Group [Text Block] | The following chart shows the relationships between (a) the compensation actually paid to the PEO, (b) the average compensation actually paid to the Non-PEO | ||
| Tabular List [Table Text Block] | The following performance measures are the Company’s most important performance measures used by us to link compensation actually paid to our NEOs for the year-end Metric Financial Performance Metric: Revenue Non-financial Delivered Test Reports Reimbursement Rates for our Tests Positive Coverage Decisions for our Tests Pipeline Milestones | ||
| Total Shareholder Return Amount | $ 68 | 125 | 195 |
| Peer Group Total Shareholder Return Amount | 113 | 125 | 125 |
| Net Income (Loss) | $ (67,138,000) | $ (31,292,000) | $ (10,284,000) |
| Company Selected Measure Amount | 137,039 | 94,085 | 62,649 |
| PEO Name | Mr. Maetzold | ||
| Measure [Axis]: 1 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Revenue | ||
| Measure [Axis]: 2 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Delivered Test Reports | ||
| Measure [Axis]: 3 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Reimbursement Rates for our Tests | ||
| Measure [Axis]: 4 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Positive Coverage Decisions for our Tests | ||
| Measure [Axis]: 5 | |||
| Pay vs Performance Disclosure [Table] | |||
| Measure Name | Pipeline Milestones | ||
| PEO [Member] | Stock Awards Value [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | $ (6,102,902) | $ (2,500,003) | $ (1,268,982) |
| PEO [Member] | Option Awards Value [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 0 | (2,656,954) | (3,056,657) |
| PEO [Member] | Change In Fair Value Of Awards Vesting During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (1,590,589) | (535,559) | 1,060,493 |
| PEO [Member] | Change In Fair Value Of Outstanding And Unvested Equity Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (3,085,629) | (4,200,151) | 6,181,735 |
| PEO [Member] | Year End Fair Value Of Equity Awards Granted During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 6,307,896 | 5,498,670 | 5,050,472 |
| Non-PEO NEO [Member] | Stock Awards Value [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (1,865,475) | (999,993) | (414,120) |
| Non-PEO NEO [Member] | Option Awards Value [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | 0 | (1,062,350) | (947,196) |
| Non-PEO NEO [Member] | Change In Fair Value Of Awards Vesting During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (549,674) | (215,497) | 332,321 |
| Non-PEO NEO [Member] | Change In Fair Value Of Outstanding And Unvested Equity Awards [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | (1,212,570) | (1,493,903) | 2,012,760 |
| Non-PEO NEO [Member] | Year End Fair Value Of Equity Awards Granted During The Year [Member] | |||
| Pay vs Performance Disclosure [Table] | |||
| Adjustment to Compensation Amount | $ 1,947,590 | $ 2,199,449 | $ 1,589,142 |
