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Fair Value Measurements - Additional Information (Detail) - TxCell S.A. - USD ($)
shares in Thousands, $ in Thousands
6 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Oct. 01, 2018
Debt Securities, Available-for-sale [Line Items]      
Liability recorded on acquisition date     $ 4,933
Share Purchase Agreement and Tender Offer Agreement      
Debt Securities, Available-for-sale [Line Items]      
Number of free shares held by the holders (in shares)     477
Estimated fair value liability of free shares     $ 200
Increase in fair value of free shares $ 500    
Estimated fair value asset of free shares $ 400    
Valuation Technique, Option Pricing Model [Member] | Share Purchase Agreement and Tender Offer Agreement      
Debt Securities, Available-for-sale [Line Items]      
Estimated fair value liability of free shares   $ 200 $ 200