Share-Based Compensation - Share-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ (8,131)	$ (13,522)
Total equity awards compensation expense	(8,503)	(13,882)
R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(2,369)	(4,025)
Total equity awards compensation expense	(2,369)	(4,025)
S&O
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(3,680)	(6,201)
Total equity awards compensation expense	(3,680)	(6,201)
G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(2,082)	(3,296)
Total equity awards compensation expense	(2,454)	(3,656)
RSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(7,976)	(12,317)
RSUs | R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(2,369)	(3,846)
RSUs | S&O
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(3,619)	(5,955)
RSUs | G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(1,988)	(2,516)
Share options / BSPCE
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(155)	(1,205)
Share options / BSPCE | R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	0	(179)
Share options / BSPCE | S&O
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(61)	(246)
Share options / BSPCE | G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	(94)	(780)
BSAs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Issuance of Stock and Warrants for Services or Claims	(372)	(360)
BSAs | R&D
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Issuance of Stock and Warrants for Services or Claims	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
BSAs | G&A
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Issuance of Stock and Warrants for Services or Claims	$ (372)	$ (360)