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, 2017	$ 1,947	$ 566,530	$ (3,800)	$ (475,318)	$ 89,359
Beginning balance (in shares) at Dec. 31, 2017	31,339,040
Increase (decrease) in shareholders' equity
Cumulative effect of retroactive implementation of ASC 606 Revenue recognition			1,802	23,116	24,918
Loss for the period				(18,789)	(18,789)
Other comprehensive loss			686		686
Exercise of share options	$ 7	1,555			1,562
Exercise of share options (in shares)	146,161
Restricted and performance share units distributed during the period	$ 17	(17)
Restricted and performance share units distributed during the period (in shares)	286,615
Share-based compensation expense		2,527			2,527
Ending balance at Mar. 31, 2018	$ 1,971	570,595	(1,312)	(470,991)	100,263
Ending balance (in shares) at Mar. 31, 2018	31,771,816
Beginning balance at Dec. 31, 2018	$ 2,299	720,072	(7,259)	(535,506)	$ 179,606
Beginning balance (in shares) at Dec. 31, 2018	37,351,653				37,351,653
Increase (decrease) in shareholders' equity
Loss for the period				(27,772)	$ (27,772)
Other comprehensive loss			(2,468)		(2,468)
Hercules warrants exercise	$ 2	1,271			1,273
Hercules warrants exercise (in shares)	37,175
Exercise of share options	$ 10	2,088			2,098
Exercise of share options (in shares)	183,807
Restricted and performance share units distributed during the period	$ 11	(11)
Restricted and performance share units distributed during the period (in shares)	188,081
Share-based compensation expense		4,294			4,294
Issuance of ordinary shares relating to employee stock purchase plan		81			81
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	3,126
Ending balance at Mar. 31, 2019	$ 2,322	$ 727,795	$ (9,727)	$ (563,278)	$ 157,112
Ending balance (in shares) at Mar. 31, 2019	37,763,842				37,763,842