Summary of business and significant accounting policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in accumulated deficit	$ 135,042	$ 45,628
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in accumulated deficit		287
Accounting Standards Update 2016-16 | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in prepaid taxes		$ 287