FORMER COLLABORATION AGREEMENT (Details) - USD ($)	Sep. 28, 2019	Sep. 30, 2020	Dec. 31, 2019
Former Collaborative Arrangement [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
Former Collaborative Arrangement
Former Collaborative Arrangement [Line Items]
Amount due to Janssen Biotech, Inc.		$ 0
Clinical Supply Agreement
Former Collaborative Arrangement [Line Items]
Amount due to Janssen Biotech, Inc.			$ 14,269,000