Balance sheet components - Purchased intangible assets (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Finite Lived Intangible Assets [Line Items]
Gross Assets	$ 54,263	$ 53,843
Accumulated Amortization	(45,564)	(43,991)
Net Assets	8,699	9,852
Technology and patents
Finite Lived Intangible Assets [Line Items]
Gross Assets	37,629	37,430
Accumulated Amortization	(32,058)	(31,061)
Net Assets	5,571	6,369
Customer relationships
Finite Lived Intangible Assets [Line Items]
Gross Assets	15,314	15,101
Accumulated Amortization	(13,189)	(12,623)
Net Assets	2,125	2,478
Leasehold interest
Finite Lived Intangible Assets [Line Items]
Gross Assets	1,320	1,312
Accumulated Amortization	(317)	(307)
Net Assets	$ 1,003	$ 1,005