Balance sheet components - Purchased Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Assets	$ 54,291		$ 54,428
Accumulated Amortization	(53,011)		(52,960)
Net Assets	1,280		1,468
Technology and patents
Finite-Lived Intangible Assets [Line Items]
Gross Assets	37,593		37,637
Accumulated Amortization	(37,154)		(37,021)
Net Assets	439		616
Amortization of Intangible Assets	200	$ 200
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Assets	15,399		15,487
Accumulated Amortization	(15,399)		(15,487)
Net Assets	0		0
Leasehold interest
Finite-Lived Intangible Assets [Line Items]
Gross Assets	1,299		1,304
Accumulated Amortization	(458)		(452)
Net Assets	$ 841		$ 852