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LICENSE AGREEMENTS (Details)			3 Months Ended		12 Months Ended
	Sep. 15, 2016 USD ($) item	Dec. 15, 2014 USD ($) item	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accrued collaboration charges					$ 1,702,000	$ 3,367,000
Collaboration revenue							$ 35,000,000
License fees and royalties					1,065,000	$ 6,162,000	$ 1,371,000
Janssen Biotech | License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received		$ 35,000,000
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%
Accrued collaboration charges					$ 1,702,000
Notification period		24 months
Maximum period Geron is obligated to procure supply for manufacturing imetelstat under collaboration agreement		9 months
Collaboration revenue				$ 35,000,000
Janssen Biotech | License agreements | U.S. Opt-In Rights exercised
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of costs to be paid by Geron		20.00%
Percentage of costs to be paid by Janssen		80.00%
Continuation Election milestone payment		$ 65,000,000
Aggregate maximum total payments for development and regulatory milestones under collaboration agreement		470,000,000
Aggregate maximum total of payments for sales milestones under collaboration agreement		$ 350,000,000
Tiered royalties percentage, low end of the range		midteens
Tiered royalties percentage, high end of the range		low twenties
U.S. selling effort percentage		20.00%
Janssen Biotech | License agreements | U.S. Opt-In Rights not exercised
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Continuation Election milestone payment		$ 65,000,000
Aggregate maximum total payments for development and regulatory milestones under collaboration agreement		415,000,000
Aggregate maximum total of payments for sales milestones under collaboration agreement		350,000,000
Full U.S. Rights fee		$ 70,000,000
Tiered royalties percentage, low end of the range		doubledigit
Tiered royalties percentage, high end of the range		midteens
Janssen Biotech | License Arrangement IP Exclusively Licensed
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of costs to be paid by Geron		50.00%
Percentage of costs to be paid by Janssen		50.00%
Janssen Pharmaceuticals Inc | License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Least number of products under License Agreement | item	1
Upfront payment received under license agreement	$ 5,000,000
Aggregate maximum total payments for development and regulatory milestones under license agreement	$ 75,000,000
Tiered royalties percentage range	low single digit
License fees and royalties			$ 5,000,000
Janssen Pharmaceuticals Inc | License Arrangement IP Exclusively Licensed
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of costs to be paid by Geron	50.00%
Percentage of costs to be paid by Janssen Pharmaceuticals	50.00%

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Carrying value as of the balance sheet date of obligations incurred and payable to collaboration partner for which invoices have not yet been received under the respective collaboration agreement (due within one year or within the normal operating cycle if longer).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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