Balance sheet components - Purchased Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Assets	$ 54,580		$ 54,580		$ 54,428
Accumulated Amortization	(53,441)		(53,441)		(52,960)
Net Assets	1,139		1,139		1,468
Technology and patents
Finite-Lived Intangible Assets [Line Items]
Gross Assets	37,778		37,778		37,637
Accumulated Amortization	(37,485)		(37,485)		(37,021)
Net Assets	293		293		616
Amortization of Intangible Assets	200	$ 200	300	$ 400
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Assets	15,484		15,484		15,487
Accumulated Amortization	(15,484)		(15,484)		(15,487)
Net Assets	0		0		0
Leasehold interest
Finite-Lived Intangible Assets [Line Items]
Gross Assets	1,318		1,318		1,304
Accumulated Amortization	(472)		(472)		(452)
Net Assets	$ 846		$ 846		$ 852