Significant accounting policies (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent	$ 637,372	$ 638,706	$ 568,136	$ 710,558	$ 772,681	$ 809,651
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent	$ (510,213)	$ (502,445)	(429,292)	$ (276,936)	$ (189,478)	(166,922)
Cumulative effect of accounting changes, net of tax
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent			(3,408)
Cumulative effect of accounting changes, net of tax | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent			$ (3,408)			$ 3,400