Summary of significant accounting policies - Long-Lived Assets in United States and Outside of United States (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property and equipment, net	$ 17,171	$ 16,006	$ 21,804
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property and equipment, net	16,845	15,491	21,236
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property and equipment, net	$ 326	$ 515	$ 568