Income tax expense - Components (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loss before income taxes attributable to domestic and international operations
Domestic									$ (78,761)	$ (113,699)	$ (66,109)
Foreign									(3,902)	(1,032)	(6,892)
Loss before income taxes									(82,663)	(114,731)	(73,001)
Current tax
Foreign									(101)	(49)	55
Deferred tax
Foreign											(1,410)
Total income tax expense	$ (21)	$ 29	$ 45	$ (154)	$ 259	$ 151	$ 48	$ (506)	$ (101)	$ (49)	$ (1,355)
Effective income tax reconciliation
Statutory income tax rate									12.50%	12.50%	12.50%
Non-deductible expenses									(0.10%)	(0.10%)	(0.80%)
Income not subject to tax									0.30%	0.30%	0.90%
Impairment											1.40%
Tax credits									0.40%	0.10%	0.20%
Foreign rate differential									0.60%	(3.10%)	21.00%
In-process research and development									0.00%	(3.50%)
Tax audit assessments									(11.80%)
Other									0.80%	0.20%	(1.40%)
Valuation allowance									(2.80%)	(6.50%)	(35.60%)
Effective income tax rate									(0.10%)	(0.10%)	(1.80%)
Ireland
Effective income tax reconciliation
Statutory income tax rate									12.50%	12.50%	12.50%