Earnings per share - Earnings Per Share, Basic and Diluted (Details) - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Ordinary Shares
Earnings per share [line items]
Basic earnings (loss) per share (USD per share)	$ 0.1720	$ 0.0061	$ (0.3539)
Diluted earnings (loss) per share (USD per share)	0.1710	0.0060	(0.3539)
American Depositary Share
Earnings per share [line items]
Basic earnings (loss) per share (USD per share)	1.03	0.04	(2.12)
Diluted earnings (loss) per share (USD per share)	$ 1.03	$ 0.04	$ (2.12)

The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator) divided by the weighted average number of ordinary shares outstanding during the period (the denominator).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of profit (loss) attributable to ordinary equity holders of the parent entity (the numerator), divided by the weighted average number of ordinary shares outstanding during the period (the denominator), both adjusted for the effects of all dilutive potential ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]]

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