Balance sheet components - Purchased intangible assets (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Finite Lived Intangible Assets [Line Items]
Gross Assets	$ 54,055	$ 53,843
Accumulated Amortization	(47,838)	(43,991)
Net Assets	6,217	9,852
Technology and Patents [Member]
Finite Lived Intangible Assets [Line Items]
Gross Assets	37,387	37,430
Accumulated Amortization	(33,463)	(31,061)
Net Assets	3,924	6,369
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Assets	15,391	15,101
Accumulated Amortization	(14,054)	(12,623)
Net Assets	1,337	2,478
Leasehold Interest [Member]
Finite Lived Intangible Assets [Line Items]
Gross Assets	1,277	1,312
Accumulated Amortization	(321)	(307)
Net Assets	$ 956	$ 1,005