Taxation - Distribution of pre-tax income by jurisdiction and components of income tax (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Distribution of pre-tax income by jurisdiction:
U.S.	$ 228,708	$ 188,503	$ 50,439
Non U.S.	137,027	1,025,649	713,972
Income (loss) before income taxes	365,735	1,214,152	764,411
Current expense:
U.S.	45,598	49,566	11,966
Non U.S.	81,371	41,921	45,614
Total current expense	126,969	91,487	57,580
Deferred expense (benefit):
U.S.	8,572	700	(56,602)
Non U.S.	(38,644)	(14,682)	33,050
Total deferred expense (benefit)	(30,072)	(13,982)	(23,552)
Total Tax Expense	$ 96,897	$ 77,505	$ 34,028