CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Cumulative Effect Adjustment Related to the Adoption of New Accounting Standards	Ordinary Shares	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Accumulated Deficit Cumulative Effect Adjustment Related to the Adoption of New Accounting Standards	Treasury Stock
BALANCE at Dec. 31, 2017	$ 1,202,808	$ (1,692)	$ 1,557	$ 2,338,755	$ (3,792)	$ (1,044,365)	$ (1,692)	$ (89,347)
BALANCE (in shares) at Dec. 31, 2017			156,057,632					(2,048,176)
Issuance of ordinary shares under employee stock plans	20,877		$ 11	20,866
Issuance of ordinary shares under employee stock plans (in shares)			1,087,815
Receipt of Alkermes' shares for the purchase of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(19,622)		$ 11	(11)				$ (19,622)
Receipt of Alkermes' shares for the purchase of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)			1,035,386					(375,313)
Share-based compensation expense	107,713			107,713
Unrealized gain on marketable securities, net of tax provision	512				512
Net loss	(139,311)					(139,311)
BALANCE at Dec. 31, 2018	1,171,285		$ 1,579	2,467,323	(3,280)	(1,185,368)		$ (108,969)
BALANCE (in shares) at Dec. 31, 2018			158,180,833					(2,423,489)
Issuance of ordinary shares under employee stock plans	18,925		$ 15	18,910
Issuance of ordinary shares under employee stock plans (in shares)			1,510,177
Receipt of Alkermes' shares for the purchase of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(9,317)		$ 8	92				$ (9,417)
Receipt of Alkermes' shares for the purchase of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)			798,878					(287,397)
Share-based compensation expense	99,705			99,705
Unrealized gain on marketable securities, net of tax provision	1,464				1,464
Net loss	(196,620)					(196,620)
BALANCE at Dec. 31, 2019	1,085,442		$ 1,602	2,586,030	(1,816)	(1,381,988)		$ (118,386)
BALANCE (in shares) at Dec. 31, 2019			160,489,888					(2,710,886)
Issuance of ordinary shares under employee stock plans	8,373		$ 7	8,366
Issuance of ordinary shares under employee stock plans (in shares)			682,122
Receipt of Alkermes' shares for the purchase of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(7,701)		$ 11	(11)				$ (7,701)
Receipt of Alkermes' shares for the purchase of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)			1,097,210					(397,193)
Share-based compensation expense	91,262			91,262
Unrealized gain on marketable securities, net of tax provision	467				467
Net loss	(110,861)					(110,861)
BALANCE at Dec. 31, 2020	$ 1,066,982		$ 1,620	$ 2,685,647	$ (1,349)	$ (1,492,849)		$ (126,087)
BALANCE (in shares) at Dec. 31, 2020			162,269,220					(3,108,079)