Other current assets - Schedule of Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Derivative instruments	$ 8,236	$ 3,324
Advances to suppliers	3,681	1,091
Receivables from statutory authorities	5,784	11,870
Others	4,632	4,883
Other current assets	$ 22,333	$ 21,168