CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Ordinary shares	Additional paid-in capital	Accumulated other comprehensive (loss)/income	Accumulated deficit	Total
Beginning balance at Dec. 31, 2019	$ 2,651	$ 986,803	$ (6,689)	$ (659,707)	$ 323,058
Beginning balance (in shares) at Dec. 31, 2019	43,711,954
Increase (decrease) in shareholders' equity
Income (Loss) for the period				(124,325)	(124,325)
Other comprehensive Income (loss)			9,022		9,022
Exercise of share options	$ 12	3,529			3,541
Exercise of share options (in shares)	211,288
Restricted and performance share units distributed during the period	$ 31	(31)
Restricted and performance share units distributed during the period (in shares)	560,986
Share-based compensation expense		16,450			16,450
Issuance of ordinary shares relating to employee stock purchase plan		147			147
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	3,282
Ending balance at Sep. 30, 2020	$ 2,694	1,006,898	2,333	(784,032)	227,893
Ending balance (in shares) at Sep. 30, 2020	44,487,510
Beginning balance at Jun. 30, 2020	$ 2,692	1,000,389	(7,319)	(730,257)	265,505
Beginning balance (in shares) at Jun. 30, 2020	44,444,405
Increase (decrease) in shareholders' equity
Income (Loss) for the period				(53,775)	(53,775)
Other comprehensive Income (loss)			9,652		9,652
Exercise of share options		139			139
Exercise of share options (in shares)	7,348
Restricted and performance share units distributed during the period	$ 2	(2)
Restricted and performance share units distributed during the period (in shares)	35,480
Share-based compensation expense		6,372			6,372
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	277
Ending balance at Sep. 30, 2020	$ 2,694	1,006,898	2,333	(784,032)	227,893
Ending balance (in shares) at Sep. 30, 2020	44,487,510
Increase (decrease) in shareholders' equity
Accumulated deficit					(784,731)
Beginning balance at Dec. 31, 2020	$ 2,711	1,016,018	9,907	(784,731)	$ 243,905
Beginning balance (in shares) at Dec. 31, 2020	44,777,799				44,777,799
Increase (decrease) in shareholders' equity
Income (Loss) for the period				321,381	$ 321,381
Other comprehensive Income (loss)			(27,790)		(27,790)
Issuance of ordinary shares	$ 55	29,510			29,565
Issuance of ordinary shares (in shares)	921,730
Tax benefit past share issuance cost		2,977			2,977
Exercise of share options	$ 10	1,814			1,824
Exercise of share options (in shares)	156,787
Restricted and performance share units distributed during the period	$ 21	(21)
Restricted and performance share units distributed during the period (in shares)	346,736
Share-based compensation expense		18,747			18,747
Issuance of ordinary shares relating to employee stock purchase plan		146			146
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	4,724
Ending balance at Sep. 30, 2021	$ 2,797	1,069,191	(17,883)	(463,350)	$ 590,755
Ending balance (in shares) at Sep. 30, 2021	46,207,776				46,207,776
Beginning balance at Jun. 30, 2021	$ 2,788	1,062,234	(4,595)	(426,819)	$ 633,608
Beginning balance (in shares) at Jun. 30, 2021	46,050,250
Increase (decrease) in shareholders' equity
Income (Loss) for the period				(36,531)	(36,531)
Other comprehensive Income (loss)			(13,288)		(13,288)
Tax benefit past share issuance cost					0
Exercise of share options	$ 5	909			914
Exercise of share options (in shares)	84,811
Restricted and performance share units distributed during the period	$ 4	(4)
Restricted and performance share units distributed during the period (in shares)	69,165
Share-based compensation expense		5,955			5,955
Issuance of ordinary shares relating to employee stock purchase plan		97			97
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	3,550
Ending balance at Sep. 30, 2021	$ 2,797	$ 1,069,191	$ (17,883)	$ (463,350)	$ 590,755
Ending balance (in shares) at Sep. 30, 2021	46,207,776				46,207,776
Increase (decrease) in shareholders' equity
Accumulated deficit					$ (463,350)