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Marketable Securities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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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 | $ 0 us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses | $ 0 us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses | $ 0 us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Other-than-temporary impairments of available-for-sale securities | $ 0 us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities | $ 0 us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities | $ 0 us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities

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- 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 No definition available. + Details
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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 + Details
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- Details
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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 + Details
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