Patents and other intangible assets - Schedule of Patents and Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Finite And Indefinite Lived Intangible Assets [Line Items]
Cost	$ 41,767	$ 39,562
Accumulated amortization	(31,946)	(32,272)
Patents and other intangible assets, net	9,821	7,290
Patents [Member]
Finite And Indefinite Lived Intangible Assets [Line Items]
Cost	41,135	38,905
Accumulated amortization	(31,487)	(31,845)
Trademarks - definite lived [Member]
Finite And Indefinite Lived Intangible Assets [Line Items]
Cost	632	657
Accumulated amortization	$ (459)	$ (427)

Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16212-109274

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph ((a)(1),(b))

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 42, 45

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant