Share-Based Compensation - Share-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ (6,457)	$ (10,816)	$ (21,392)	$ (35,700)
Total equity awards compensation expense	(6,803)	(11,165)	(22,465)	(36,760)
R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(3,333)	(3,212)	(7,771)	(10,565)
Total equity awards compensation expense	(3,333)	(3,212)	(7,771)	(10,565)
S&O
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(3,190)	(3,809)	(8,380)	(13,902)
Total equity awards compensation expense	(3,190)	(3,809)	(8,380)	(13,902)
G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	66	(3,795)	(5,241)	(11,233)
Total equity awards compensation expense	(280)	(4,144)	(6,314)	(12,293)
RSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(6,885)	(10,291)	(21,031)	(34,725)
RSUs | R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(3,333)	(3,190)	(7,771)	(10,988)
RSUs | S&O
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(2,957)	(3,741)	(8,092)	(14,365)
RSUs | G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(595)	(3,360)	(5,168)	(9,372)
Share options / BSPCE
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	428	(525)	(361)	(975)
Share options / BSPCE | R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	0	(22)		423
Share options / BSPCE | S&O
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(233)	(68)	(288)	463
Share options / BSPCE | G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	661	(435)	(73)	(1,861)
BSAs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Issuance of Stock and Warrants for Services or Claims	(346)	(349)	(1,073)	(1,060)
BSAs | R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Issuance of Stock and Warrants for Services or Claims	0	0	0	0
BSAs | S&O
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Issuance of Stock and Warrants for Services or Claims	0	0	0	0
BSAs | G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Issuance of Stock and Warrants for Services or Claims	$ (346)	$ (349)	$ (1,073)	$ (1,060)