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Summary of significant accounting policies (Details 2)
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6 Months Ended |
|---|---|
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Jun. 30, 2012
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| Revenue recognition | |
| Percentage of sales withheld for future refunds, prior contract terms | 3.00% |
| Period for which sales are withheld for future refunds, prior contract terms | 6 months |
|
Platform service arrangements | Minimum
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| Revenue recognition | |
| Term of the arrangement used to determine revenue recognition | 2 years |
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Platform service arrangements | Maximum
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|
| Revenue recognition | |
| Term of the arrangement used to determine revenue recognition | 5 years |
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Wholesale partner arrangement | Minimum
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|
| Revenue recognition | |
| Term of the arrangement used to determine revenue recognition | 5 years |
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Wholesale partner arrangement | Maximum
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| Revenue recognition | |
| Term of the arrangement used to determine revenue recognition | 10 years |