STOCKHOLDERS' EQUITY (Details 10) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
401(k) Plan
Matching contribution by employer (as a percent)	100.00%	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	$ 539,000
Geron 401K Plan
401(k) Plan
Operating expenses as a result of accelerated vesting of unvested prior employer matches for employees affected by the November 2011 restructuring	370,000
Research and development | Geron 401K Plan
401(k) Plan
Operating expense recorded for vested portion of employer matching contribution	616,000	1,179,000	1,051,000
General and administrative | Geron 401K Plan
401(k) Plan
Operating expense recorded for vested portion of employer matching contribution	$ 259,000	288,000	243,000