Cash and stock-based compensation plans (Details 2)	12 Months Ended
Dec. 31, 2017 USD ($) Year	Dec. 31, 2016 USD ($) Year	Dec. 31, 2015 USD ($) Year
Disclosure Of Sharebased Payment Arrangements [Line Items]
Weighted average fair value per option	$ 0	$ 0
Weighted average expected term, in years \| Year	0	0	5.5
Expected volatility	0.00%	0.00%	22.00%
Risk-free rate	0.00%	0.00%
Expected dividend	0.00%	0.00%	5.00%
Bottom of range [member]
Disclosure Of Sharebased Payment Arrangements [Line Items]
Weighted average fair value per option			$ 1.95
Risk-free rate			0.02%
Top of range [member]
Disclosure Of Sharebased Payment Arrangements [Line Items]
Weighted average fair value per option			$ 2.06
Risk-free rate			1.52%

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- Definition

The expected volatility of the share price used to calculate the fair value of the share options granted. Expected volatility is a measure of the amount by which a price is expected to fluctuate during a period. The measure of volatility used in option pricing models is the annualised standard deviation of the continuously compounded rates of return on the share over a period of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2017-01-01
-Paragraph 47
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_a_i&doctype=Standard
-URIDate 2017-03-09

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- Definition

The option life of share options granted.

+ References

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- Definition

The implied yield currently available on zero-coupon government issues of the country in whose currency the exercise price for share options granted is expressed, with a remaining term equal to the expected term of the option being valued (based on the option's remaining contractual life and taking into account the effects of expected early exercise). [Refer: Government [member]]

+ References

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- Definition

The percentage of an expected dividend used to calculate the fair value of share options granted.

+ References

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- Definition

The weighted average fair value of share options granted during the period at the measurement date. [Refer: Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2017-01-01
-Paragraph 47
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_a&doctype=Standard
-URIDate 2017-03-09

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