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Marketable Securities - Additional Information (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract] |  |  |
Realized losses from the sale of available-for-sale securities | $ 0 | $ 0 | $ 0
Investments other-than-temporarily impaired | $ 0 | $ 0 |

X
- Definition Other than temporarily impaired investment. + References No definition available. + Details
Name: | sgmo_OtherThanTemporarilyImpairedInvestment
Namespace Prefix: | sgmo_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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 No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration