STOCKHOLDERS' EQUITY - 2023 At Market Issuance Sales Agreement (Details) - 2023 Sales Agreement - Subsequent Event	Nov. 01, 2023 USD ($)
At Market Issuance Sales Agreements [Line Items]
Aggregate offering price of common stock	$ 100,000,000
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 sales agent under the sales agreement.

No definition available.

Name:	gern_MaximumCommissionRate
Namespace Prefix:	gern_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration