Taxation - Distribution of pre-tax income by jurisdiction and components of income tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Distribution of pre-tax income by jurisdiction:
U.S.	$ (5,931)	$ 228,708	$ 188,503
Non U.S.	1,300,109	137,027	1,025,649
Income (loss) before income taxes	1,294,178	365,735	1,214,152
Current expense:
U.S.	(22,698)	45,598	49,566
Non U.S.	67,784	81,371	41,921
Total current expense	45,086	126,969	91,487
Deferred expense (benefit):
U.S.	(63,491)	8,572	700
Non U.S.	(756)	(38,644)	(14,682)
Total deferred expense (benefit)	(64,247)	(30,072)	(13,982)
Total tax expense	$ (19,161)	$ 96,897	$ 77,505