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Marketable Securities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Investments maturity period	2 years
Available for sale securities maturity percentage next twelve months	79.00%sgmo_AvailableForSaleSecuritiesMaturityPercentageNextTwelveMonths
Available for sale securities maturity percentage in twelve and twenty four months	21.00%sgmo_AvailableForSaleSecuritiesMaturityPercentageInNextTwelveMonthsAndYearTwo
Realized losses	$ 0us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses	$ 0us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses	$ 0us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Other-than-temporary impairments of available-for-sale securities	$ 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities	$ 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities	$ 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities

X

- Definition

Available for sale securities maturity percentage in next twelve months and year two.

+ References

No definition available.

+ Details

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- Definition

Available for sale securities maturity percentage next twelve months.

+ References

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- Definition

Investments maturity dates available for sale securities.

+ References

No definition available.

+ Details

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- Definition

This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ 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 (a)

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

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- Definition

The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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