Summary of significant accounting policies (Details 3)	12 Months Ended
Dec. 31, 2011 unit
Finite lived intangible assets
Number of reporting units	3
Developed technologies
Finite lived intangible assets
Weighted average amortization period (in years)	11
Distribution networks
Finite lived intangible assets
Weighted average amortization period (in years)	10

The average useful life of a major finite-lived intangible asset class. A major class is composed of intangible assets that can be grouped together because they are similar either by their nature or by their use in the operations of a company.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=6905858&loc=d3e16265-109275

Name:	us-gaap_FiniteLivedIntangibleAssetsAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration