CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS DATA (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012
Supplemental Operating Activities:
Issuance of common stock for 401(k) matching contributions	$ 839	$ 1,361
Issuance of common stock for services rendered to date or to be received in future periods		69
Reclassification of deposits to other current assets, net	219	135
Supplemental Investing Activities:
Net unrealized (loss) gain on available-for-sale securities	$ (52)	$ 4

Represents the amount of deposits that are expected to be returned within one year and are therefore reclassified to other current assets.

No definition available.

+ Details

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Namespace Prefix:	gern_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Definition

This item represents the pretax change in net unrealized holding gain (loss) on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

+ Details

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- Definition

Value of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan.

+ References

No definition available.

+ Details

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Balance Type:	credit
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- Definition

Value of stock issued in lieu of cash for services contributed to the entity. Value of the stock issued includes, but is not limited to, services contributed by vendors and founders.

+ References

No definition available.

+ Details

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