Fair Value Measurements - Summary of Estimated Fair Value of Free Shares Valuation Assumptions (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2019 $ / shares	Dec. 31, 2018 $ / shares	Mar. 31, 2019 € / shares	Dec. 31, 2018 € / shares	Oct. 01, 2018 $ / shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price (USD)	$ 9.54	$ 11.48
Stock Price (EUR)					$ 2.99
EUR/ USD Exchange Rate	0.89	0.87	0.89	0.87
Stock Price Volatility Estimate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Volatility Estimate	87.7	79.9	87.7	79.9
Exchange Rate Volatility Estimate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Volatility Estimate	7.2	7.7	7.2	7.7
Risk Free Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Risk Free Rate	Varies by expected exercise date	Varies by expected exercise date
TxCell S.A. [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price (EUR) | (per share)		$ 2.94	€ 2.36	€ 2.58	$ 2.99
TxCell S.A. [Member] | Estimated Correlation Sangamo [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Volatility Estimate	50.0		50.0
TxCell S.A. [Member] | Stock Price Volatility Estimate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Volatility Estimate	82.8	8.6	82.8	8.6