Taxation - Distribution of pre-tax income by jurisdiction and components of income tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Distribution of pre-tax income by jurisdiction:
U.S.	$ 68,970	$ (5,931)	$ 228,708
Non U.S.	543,304	1,300,109	137,027
Income (loss) before income taxes	612,274	1,294,178	365,735
Current expense:
U.S.	(12,201)	(22,698)	45,598
Non U.S.	59,031	67,784	81,371
Total current expense	46,830	45,086	126,969
Deferred expense (benefit):
U.S.	8,502	(63,491)	8,572
Non U.S.	(13,203)	(756)	(38,644)
Total deferred expense (benefit)	(4,701)	(64,247)	(30,072)
Total tax expense	$ 42,129	$ (19,161)	$ 96,897