Summary of significant accounting policies - Practical expedient (Details) |
3 Months Ended |
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Mar. 31, 2018 | |
| Summary of significant accounting policies | |
| Practical expedient of financing component | true |
| Practical expedient of incremental cost | true |
| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Indicates (true/false) whether practical expedient is elected not to adjust consideration for effect of financing component when transfer and customer payment of good or service occurs within one year or less. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition Indicates (true/false) whether practical expedient is elected to recognize incremental cost of obtaining contract as expense when incurred if amortization period would have been one year or less. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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