Income tax expense - Net Operating Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net operating losses carryforwards
Period in which the company is in cumulative loss position.	3 years
Valuation allowance	$ 116,200	$ 103,185	$ 100,832	$ 80,087
Uncertain tax positions disclosures
Uncertain tax positions	0
Ireland
Net operating losses carryforwards
Net operating losses carryforwards	251,775
Austria
Net operating losses carryforwards
Net operating losses carryforwards	248,563
U.S.
Net operating losses carryforwards
Net operating losses carryforwards	10,401
Net operating losses carryforwards	$ 35,516