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STOCKHOLDERS' EQUITY (Details 10) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
401(k) Plan      
Matching contribution by employer (as a percent) 75.00% 100.00% 100.00%
Period of vesting of matching contributions 4 years 4 years 4 years
Service period of employees 4 years 4 years 4 years
Unvested amount under the defined-contribution savings plan to be amortized $ 369,000    
Geron 401K Plan
      
401(k) Plan      
Operating expenses as a result of accelerated vesting of unvested prior employer matches for employees affected by recent restructurings 266,000 370,000  
Research and development | Geron 401K Plan
      
401(k) Plan      
Operating expense recorded for vested portion of employer matching contribution 156,000 616,000 1,179,000
General and administrative | Geron 401K Plan
      
401(k) Plan      
Operating expense recorded for vested portion of employer matching contribution $ 157,000 $ 259,000 $ 288,000