Revenue, deferred revenue, and deferred commissions - Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other receivables	$ 6,263		$ 6,312
Deferred revenue, current	47,884		50,033
Deferred revenue, long-term	9,524		11,442
Total deferred revenue	57,408	$ 54,014	61,475
Stockholders' equity	$ 171,702		$ 163,825