Balance sheet components - Property, Plant and Equipment, net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 246,483,000	$ 252,667,000
Less: Accumulated depreciation	(146,393,000)	(125,102,000)
Property, plant and equipment, net	100,090,000	127,565,000
Depreciation expense	29,900,000	27,000,000	$ 17,900,000
Asset impairment charges	1,000,000	400,000	0
Purchases of property, plant and equipment, unpaid	1,500,000	10,000,000	$ 16,100,000
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment	3,157,000	3,083,000
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment	23,379,000	24,102,000
Asset impairment charges		100,000
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment	187,746,000	189,527,000
Furniture, fixtures, software and office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment	10,201,000	9,948,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 22,000,000	$ 26,007,000