CONSOLIDATED STATEMENTS OF SHAREHOLDERS' DEFICIT - USD ($) shares in Thousands, $ in Thousands	Ordinary Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balances at Dec. 31, 2018	$ 1	$ 960,721	$ (166)	$ (1,012,145)	$ (51,589)
Balances (in shares) at Dec. 31, 2018	55,681
Increase (Decrease) in Stockholders' Equity
Proceeds from ESPP purchases		3,474			3,474
Proceeds from ESPP purchases (in shares)	203
Employee share-based compensation expense		60,450			60,450
Issuance of restricted shares (in shares)	1,105
Option exercises		3,142			3,142
Option exercises (in shares)	164
Repurchase of shares to satisfy tax withholding		(3,173)			(3,173)
Repurchase of shares to satisfy tax withholding (in shares)	(138)
Net unrealized gain (loss) on marketable securities			311		311
Net loss				(236,455)	(236,455)
Balances at Dec. 31, 2019	$ 1	1,024,614	145	(1,248,600)	(223,840)
Balances (in shares) at Dec. 31, 2019	57,015
Increase (Decrease) in Stockholders' Equity
Net proceeds from sale of ordinary shares		139,915			139,915
Net proceeds from sale of ordinary shares (in shares)	5,500
Proceeds from ESPP purchases		3,701			3,701
Proceeds from ESPP purchases (in shares)	245
Employee share-based compensation expense		62,976			62,976
Issuance of restricted shares (in shares)	1,907
Option exercises		1,361			1,361
Option exercises (in shares)	68
Repurchase of shares to satisfy tax withholding		(9,749)			(9,749)
Repurchase of shares to satisfy tax withholding (in shares)	(407)
Net unrealized gain (loss) on marketable securities			(98)		(98)
Net loss				(278,017)	(278,017)
Balances at Dec. 31, 2020	$ 1	1,222,818	47	(1,526,617)	$ (303,751)
Balances (in shares) at Dec. 31, 2020	64,328				64,328
Increase (Decrease) in Stockholders' Equity
Net proceeds from sale of ordinary shares		108,180			$ 108,180
Net proceeds from sale of ordinary shares (in shares)	7,705
Proceeds from ESPP purchases		3,466			3,466
Proceeds from ESPP purchases (in shares)	275
Employee share-based compensation expense		62,061			62,061
Issuance of restricted shares (in shares)	2,682
Option exercises		5			5
Repurchase of shares to satisfy tax withholding		(9,061)			(9,061)
Repurchase of shares to satisfy tax withholding (in shares)	(555)
Net unrealized gain (loss) on marketable securities			$ (47)		(47)
Net loss				(199,426)	(199,426)
Balances at Dec. 31, 2021	$ 1	$ 1,387,469		$ (1,726,043)	$ (338,573)
Balances (in shares) at Dec. 31, 2021	74,435				74,435