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Significant accounting policies - Intangible assets (Details)	12 Months Ended
	Dec. 31, 2018
Internal-use software
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life	4 years
Customer contracts | Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life	1 year
Customer contracts | Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life	2 years
Favourable land lease
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life	27 years
Assembled workforce
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life	5 years
Partnership relationship
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life	5 years
Brand
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life	5 years

X

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- 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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- Details

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- Details

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- Details

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- Details

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