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Fair Value Measurement - Summary of Estimated Fair Value of Free Share Liability Assumptions (Detail)	12 Months Ended
	Dec. 31, 2019 $ / shares	Dec. 31, 2018 $ / shares	Dec. 31, 2019 € / shares	Oct. 01, 2018 $ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
USD/ EUR Exchange Rate	0.91	0.87	0.91
Measurement Input, Share Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sangamo Stock Price (USD) (in usd per share)	$ 8.68	$ 11.48
Stock Price Volatility Estimate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Volatility Estimate	0.725	0.799	0.725
Exchange Rate Volatility Estimate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Volatility Estimate	0.066	0.077	0.066
Risk Free Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Risk Free Rate and Cost of Debt by Expected Exercise Date	Varies	Varies
TxCell S.A.
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sangamo France Stock Price (EUR) (in Euro per share)				$ 2.99
TxCell S.A. | Measurement Input, Share Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sangamo France Stock Price (EUR) (in Euro per share) | (per share)		$ 2.58	€ 2.14
TxCell S.A. | Stock Price Volatility Estimate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Volatility Estimate	0.725	0.086	0.725
TxCell S.A. | Measurement Input Stock Price Correlation
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated Correlation Sangamo and Sangamo France Stock Prices	1.000	0	1.000

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Foreign exchange rate used to translate amounts denominated in functional currency to reporting currency.

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