Income per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income attributable to the parent company’s common shareholders - Basic and Diluted	$ 4,288	$ 6,733	$ 20,456	$ 24,514
Denominator:
Weighted average shares outstanding	32,121,019	28,043,019	32,121,019	28,043,019
Dilutive effects of stock options	13,820	20,642	14,984	20,827
Denominator for dilutive income per share - Diluted	32,134,839	28,063,661	32,136,003	28,063,846
Net income per share attributable to the parent company's common shareholders
Net income per share attributable to parent company’s common shareholders - Basic	$ 0.13	$ 0.24	$ 0.64	$ 0.87
Net income per share attributable to parent company’s common shareholders - Diluted	$ 0.13	$ 0.24	$ 0.64	$ 0.87