Other current assets - Schedule of Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Derivative instruments	$ 8,826	$ 3,324
Advances to suppliers	1,601	1,091
Receivables from statutory authorities	4,787	11,870
Others	3,570	4,883
Other current assets	$ 18,784	$ 21,168