Taxation - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of the year	$ 80,590	$ 37,190	$ 30,000
Increases for tax positions taken during the year	25,250	20,370	12,182
Increases for tax positions taken in prior years	11,700	38,650	15,304
Decreases for tax positions taken in prior years	(6,440)	(4,850)	(20,296)
Decreases for lapse of the applicable statute of limitations	(13,320)	(10,770)	0
Unrecognized tax benefits, end of the year	$ 97,780	$ 80,590	$ 37,190