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LICENSE AGREEMENTS (Details) | Sep. 29, 2018 | Nov. 13, 2014 item | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
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Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |
Percentage of costs to be paid by Geron after termination of Collaboration Agreement | 100.00% |  |  |
Amount due to Janssen Biotech, Inc. |  |  |  | $ 14,269,000
Clinical Supply Agreement |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |
Amount due to Janssen Biotech, Inc. |  |  | $ 0 | $ 14,269,000
Janssen Biotech | Former Collaboration Agreement |  |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |  |
Number of agreed upon studies | item |  | 2 |  |
Percentage of costs to be paid by Geron |  | 50.00% |  |
Percentage of costs to be paid by Janssen |  | 50.00% |  |

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