Revenue, deferred revenue, and deferred commissions - Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other receivables	$ 6,645		$ 6,312
Deferred revenue, current	43,841		50,033
Deferred revenue, long-term	10,173		11,442
Total deferred revenue	54,014	$ 56,676	61,475
Stockholders' equity	$ 160,655		$ 163,825