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Income Taxes - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Income Taxes [Line Items]      
Income tax expense $ 0us-gaap_IncomeTaxExpenseBenefit    
Statutory tax rate 34.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate    
Valuation allowance 112,899,000us-gaap_DeferredTaxAssetsValuationAllowance 103,107,000us-gaap_DeferredTaxAssetsValuationAllowance  
Increase in deferred tax assets valuation allowance 9,800,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount 14,900,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount 5,400,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount
Deferred tax assets, net operating loss carryforwards for federal 330,900,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic    
Deferred tax assets, net operating loss carryforwards for state 278,100,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal    
Federal research tax credit carryforwards 6,700,000sgmo_DeferredTaxAssetsTaxCreditCarryforwardsResearchFederal    
State research tax credit carryforwards 7,000,000sgmo_DeferredTaxAssetsTaxCreditCarryforwardsResearchStateAndLocal    
Tax credit carryforward, expiration year 2018    
Accrued interest and/or penalties 0us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued    
State      
Income Taxes [Line Items]      
Operating loss carryforwards, expiration year 2015    
Federal      
Income Taxes [Line Items]      
Operating loss carryforwards, expiration year 2018    
Indefinite-lived assets [Member]      
Income Taxes [Line Items]      
Valuation allowance $ 0us-gaap_DeferredTaxAssetsValuationAllowance
/ us-gaap_ValuationAllowanceByDeferredTaxAssetAxis
= us-gaap_IndefinitelivedIntangibleAssetsMember