Taxation (Income Tax Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected income tax benefit									$ 14,216	$ 4,856	$ 1,011
Tax exempt income									3,794	4,487	4,939
Non-taxable foreign exchange gains (losses)									2,574	(1,126)	(1,897)
Transaction costs									0	(131)	3,654
Withholding tax									(216)	(2,578)	(3,036)
Change in valuation allowance									(11,718)	(924)	43,808
Effect of change in tax rate									(38,083)	0	0
Other									2,946	(4,924)	(2,613)
Income tax (expense) benefit	$ (41,226)	$ 18,977	$ (3,904)	$ (334)	$ 7,700	$ 1,316	$ (6,612)	$ (2,744)	$ (26,487)	$ (340)	$ 45,866