Balance sheet components - Purchased intangible assets (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Gross Assets	$ 53,663	$ 53,183
Accumulated Amortization	(48,765)	(47,621)
Net Assets	4,898	5,562
Technology and Patents [Member]
Finite Lived Intangible Assets [Line Items]
Gross Assets	37,200	36,918
Accumulated Amortization	(34,048)	(33,316)
Net Assets	3,152	3,602
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Assets	15,207	15,039
Accumulated Amortization	(14,380)	(13,990)
Net Assets	827	1,049
Leasehold Interest [Member]
Finite Lived Intangible Assets [Line Items]
Gross Assets	1,256	1,226
Accumulated Amortization	(337)	(315)
Net Assets	$ 919	$ 911

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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