Balance sheet components - Purchased Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Assets	$ 54,572		$ 54,572		$ 54,428
Accumulated Amortization	(53,587)		(53,587)		(52,960)
Net Assets	985		985		1,468
Technology and patents
Finite-Lived Intangible Assets [Line Items]
Gross Assets	37,777		37,777		37,637
Accumulated Amortization	(37,631)		(37,631)		(37,021)
Net Assets	146		146		616
Amortization of Intangible Assets	200	$ 200	500	$ 600
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Assets	15,476		15,476		15,487
Accumulated Amortization	(15,476)		(15,476)		(15,487)
Net Assets	0		0		0
Leasehold interest
Finite-Lived Intangible Assets [Line Items]
Gross Assets	1,319		1,319		1,304
Accumulated Amortization	(480)		(480)		(452)
Net Assets	$ 839		$ 839		$ 852