Segment and geographic information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 81,133	$ 100,090
China
Segment Reporting Information [Line Items]
Property, plant and equipment, net	19,230	27,329
United States
Segment Reporting Information [Line Items]
Property, plant and equipment, net	26,068	29,054
Japan
Segment Reporting Information [Line Items]
Property, plant and equipment, net	25,772	29,631
Rest of world
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 10,063	$ 14,076