Income tax (expense) benefit - Components (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss before income taxes attributable to domestic and international operations
Domestic									$ (113,699)	$ (66,109)	$ (54,509)
Foreign									(1,032)	(6,892)	(1,053)
Loss before income taxes									(114,731)	(73,001)	(55,562)
Current tax
Domestic											(4)
Foreign									(49)	55	(118)
Deferred tax
Foreign										(1,410)	794
Total income tax (expense) benefit	$ 259	$ 151	$ 48	$ (506)	$ (101)	$ (1,872)	$ 967	$ (349)	$ (49)	$ (1,355)	$ 672
Effective income tax reconciliation
Statutory income tax rate									12.50%	12.50%	25.00%
Non-deductible expenses									(0.10%)	(0.80%)	(0.20%)
Income not subject to tax									0.30%	0.90%	2.80%
Impairment										1.40%
Tax credits									0.10%	0.20%	0.40%
Foreign rate differential									(3.10%)	21.00%	(2.50%)
In-process research and development									(3.50%)
Other									0.20%	(1.40%)	0.20%
Valuation allowance									(6.50%)	(35.60%)	(24.50%)
Effective income tax rate									(0.10%)	(1.80%)	1.20%
Austria
Effective income tax reconciliation
Statutory income tax rate											25.00%
Ireland
Effective income tax reconciliation
Statutory income tax rate									12.50%	12.50%