Income per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Numerator:
Net income attributable to the parent company’s common shareholders - Basic and Diluted	$ 5,059	$ 5,682	$ 19,694	$ 16,755	$ 22,511
Denominator:
Weighted average shares outstanding	31,644,004	31,911,360	31,644,004	32,038,933
Dilutive effects of stock options	267	362	3,829	1,581
Denominator for dilutive income per share - Diluted	31,644,271	31,911,722	31,647,833	32,040,514
Net income per share attributable to parent company’s common shareholders
Basic	$ 0.16	$ 0.18	$ 0.62	$ 0.52
Diluted	$ 0.16	$ 0.18	$ 0.62	$ 0.52