Summary of significant accounting policies - Recent Pronouncements (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jan. 01, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets	$ 22,892
Operating lease liabilities - non-current	$ 21,442
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets		$ 25,000
Operating lease liabilities - non-current		$ 28,600