Fair Value Measurement - Additional Information (Detail)		12 Months Ended
	Oct. 01, 2018 $ / shares shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2018 € / shares	Oct. 01, 2018 € / shares shares
Schedule Of Available For Sale Securities [Line Items]
Number of free shares held by the holders	477,000,000			477,000,000
TxCell S.A. [Member]
Schedule Of Available For Sale Securities [Line Items]
Free shares options purchase price per share | (per share)	$ 2.99	$ 2.94	€ 2.58
TxCell S.A. [Member] | Share Purchase Agreement and Tender Offer Agreement [Member]
Schedule Of Available For Sale Securities [Line Items]
Number of free shares held by the holders	477,000			477,000
Free shares options purchase price per share | (per share)	$ 2.99			€ 2.58
Exchange rate on purchase price	1.16
Changes in fair value of free share liability | $		$ 0