STOCKHOLDERS' EQUITY - SALES AGREEMENT (Details)	Aug. 28, 2015 USD ($)
STOCKHOLDERS' EQUITY
Aggregate offering price of common stock	$ 50,000,000
Maximum commission rate (as a percent)	3.00%

Represents the percentage of maximum commission rate, based on gross proceeds of sale price per share of common stock sold through MLV & Co. under the sales agreement.

No definition available.

Name:	gern_MaximumCommissionRate
Namespace Prefix:	gern_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration