Balance sheet components - Purchased Itangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Assets	$ 52,890	$ 53,191
Accumulated Amortization	(50,937)	(51,040)
Net Assets	1,953	2,151
Technology and patents
Finite-Lived Intangible Assets [Line Items]
Gross Assets	36,685	36,880
Accumulated Amortization	(35,537)	(35,555)
Net Assets	1,148	1,325
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Assets	15,004	15,089
Accumulated Amortization	(15,004)	(15,089)
Net Assets	0	0
Leasehold interest
Finite-Lived Intangible Assets [Line Items]
Gross Assets	1,201	1,222
Accumulated Amortization	(396)	(396)
Net Assets	$ 805	$ 826