Balance sheet components - Purchased Itangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Assets	$ 52,772	$ 53,413
Accumulated Amortization	(50,457)	(50,395)
Net Assets	2,315	3,018
Technology and patents
Finite-Lived Intangible Assets [Line Items]
Gross Assets	36,609	37,029
Accumulated Amortization	(35,107)	(34,995)
Net Assets	1,502	2,034
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Assets	14,970	15,146
Accumulated Amortization	(14,970)	(15,026)
Net Assets	0	120
Leasehold interest
Finite-Lived Intangible Assets [Line Items]
Gross Assets	1,193	1,238
Accumulated Amortization	(380)	(374)
Net Assets	$ 813	$ 864