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, 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 exercise 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 on marketable securities, net of tax provision	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)
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)
Unrealized gain on marketable securities, net of tax provision	1,666
Net loss	(138,388)
BALANCE at Jun. 30, 2019	1,091,168	$ 1,595	2,533,086	(1,614)	(1,323,756)	$ (118,143)
BALANCE (in shares) at Jun. 30, 2019		159,796,116				(2,699,243)
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)
Issuance of ordinary shares under employee stock plans	2,054	$ 2	2,052
Issuance of ordinary shares under employee stock plans (in shares)		197,953
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(194)					$ (194)
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)		20,289				(6,397)
Share-based compensation expense	28,261		28,261
Unrealized gain on marketable securities, net of tax provision	896			896
Net loss	(41,990)				(41,990)
BALANCE at Jun. 30, 2019	1,091,168	$ 1,595	2,533,086	(1,614)	(1,323,756)	$ (118,143)
BALANCE (in shares) at Jun. 30, 2019		159,796,116				(2,699,243)
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	3,071	$ 3	3,068
Issuance of ordinary shares under employee stock plans (in shares)		258,137
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(7,283)	$ 10	(10)			$ (7,283)
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)		1,020,510				(372,846)
Share-based compensation expense	20,125		20,125
Unrealized gain on marketable securities, net of tax provision	317			317
Net loss	(38,654)				(38,654)
BALANCE at Mar. 31, 2020	1,063,018	$ 1,615	2,609,213	(1,499)	(1,420,642)	$ (125,669)
BALANCE (in shares) at Mar. 31, 2020		161,768,535				(3,083,732)
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)
Unrealized gain on marketable securities, net of tax provision	1,715
Net loss	(68,085)
BALANCE at Jun. 30, 2020	1,061,846	$ 1,618	2,636,194	(101)	(1,450,073)	$ (125,792)
BALANCE (in shares) at Jun. 30, 2020		162,119,961				(3,091,606)
BALANCE at Mar. 31, 2020	1,063,018	$ 1,615	2,609,213	(1,499)	(1,420,642)	$ (125,669)
BALANCE (in shares) at Mar. 31, 2020		161,768,535				(3,083,732)
Issuance of ordinary shares under employee stock plans	3,848	$ 3	3,845
Issuance of ordinary shares under employee stock plans (in shares)		327,251
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share-based awards	(123)					$ (123)
Receipt of Alkermes' shares for the exercise of stock options or to satisfy minimum tax withholding obligations related to share based awards (in shares)		24,175				(7,874)
Share-based compensation expense	23,136		23,136
Unrealized gain on marketable securities, net of tax provision	1,398			1,398
Net loss	(29,431)				(29,431)
BALANCE at Jun. 30, 2020	$ 1,061,846	$ 1,618	$ 2,636,194	$ (101)	$ (1,450,073)	$ (125,792)
BALANCE (in shares) at Jun. 30, 2020		162,119,961				(3,091,606)