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Significant accounting policies - Revenue recognition (Details)	12 Months Ended
	Dec. 31, 2016
Minimum
Property, Plant and Equipment [Line Items]
Term of contract (less than one year)	1 year

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- Definition

Term of Contract

+ References

No definition available.

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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