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v3.19.1

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 |

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