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Marketable Securities - Additional Information (Detail) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018
Investments Debt And Equity Securities [Abstract] |  |  |
Investments maturity period | 1 year |  | 1 year
Realized losses of available-for-sale securities | $ 0 | $ 0 |
Investments other-than-temporarily impaired | $ 0 |  | $ 0

X
- Definition Investments maturity dates available for sale securities. + References No definition available. + Details
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Namespace Prefix: | sgmo_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Other than temporarily impaired investment. + References No definition available. + Details
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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

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