CONDENSED 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
Employee share-based compensation expense		12,220			12,220
Issuance of restricted shares (in shares)	426
Option exercises		254			254
Option exercises (in shares)	15
Repurchase of shares to satisfy tax withholding		(1,687)			(1,687)
Net unrealized gain on available-for-sale investments			130		130
Net loss				(72,580)	(72,580)
Balances at Mar. 31, 2019	$ 1	971,508	(36)	(1,084,725)	(113,252)
Balances (in shares) at Mar. 31, 2019	56,122
Balances at Dec. 31, 2019	$ 1	1,024,614	145	(1,248,600)	$ (223,840)
Balances (in shares) at Dec. 31, 2019	57,015				57,015
Increase (Decrease) in Stockholders' Equity
Proceeds from sale of ordinary shares		139,915			$ 139,915
Number of shares sold	5,500
Employee share-based compensation expense		15,276			15,276
Issuance of restricted shares (in shares)	744
Option exercises		203			203
Option exercises (in shares)	8
Repurchase of shares to satisfy tax withholding		(6,804)			(6,804)
Repurchase of shares to satisfy tax withholding (in shares)	(263)
Net unrealized gain on available-for-sale investments			367		367
Net loss				(83,053)	(83,053)
Balances at Mar. 31, 2020	$ 1	$ 1,173,204	$ 512	$ (1,331,653)	$ (157,936)
Balances (in shares) at Mar. 31, 2020	63,004				63,004