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ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CASH EQUIVALENTS AND MARKETABLE SECURITIES (Details)	12 Months Ended
	Dec. 31, 2016
Minimum
Marketable securities
Original maturity period of marketable securities	4 months
Maximum
Marketable securities
Original maturity period of marketable securities	24 months

X

- Definition

Represents the original maturity period of securities, which are categorized neither as held-to-maturity nor trading.

+ References

No definition available.

+ Details

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Namespace Prefix:	gern_
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Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: