CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Ordinary Shares	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Treasury Stock
BALANCE at Dec. 31, 2017	$ 1,202,808	$ 1,557	$ 2,338,755	$ (3,792)	$ (1,044,365)	$ (89,347)
BALANCE (in shares) at Dec. 31, 2017		156,057,632				(2,048,176)
Issuance of ordinary shares under employee stock plans	13,165	$ 6	13,159
Issuance of ordinary shares under employee stock plans (in shares)		539,563
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(15,724)	$ 7	(7)			$ (15,724)
Receipt of Alkermes' shares for the excersise of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)		716,123				(261,159)
Share-based compensation expense	20,176		20,176
Unrealized gain (loss) on marketable securities, net of tax provision of $229	(337)			(337)
Cumulative effect adjustment related to the adoption of new accounting standards	(1,692)				(1,692)
Net loss	(62,505)				(62,505)
BALANCE at Mar. 31, 2018	1,155,891	$ 1,570	2,372,083	(4,129)	(1,108,562)	$ (105,071)
BALANCE (in shares) at Mar. 31, 2018		157,313,318				(2,309,335)
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	10,554	$ 7	10,547
Issuance of ordinary shares under employee stock plans (in shares)		656,352
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(8,880)	$ 7	93			$ (8,980)
Receipt of Alkermes' shares for the excersise of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)		740,689				(269,357)
Share-based compensation expense	24,810		24,810
Unrealized gain (loss) on marketable securities, net of tax provision of $229	770			770
Net loss	(96,398)				(96,398)
BALANCE at Mar. 31, 2019	$ 1,102,141	$ 1,593	$ 2,502,773	$ (2,510)	$ (1,281,766)	$ (117,949)
BALANCE (in shares) at Mar. 31, 2019		159,577,874				(2,692,846)