Taxation (Income Tax Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Expected income tax benefit									$ 17,697	$ 14,216	$ 4,856
Tax exempt income									944	3,794	4,487
Non-taxable foreign exchange gains (losses)									586	2,574	(1,126)
Effect of change in tax rate									(708)	(38,083)	(1,421)
U.S. base erosion and anti-abuse tax									(1,271)	0	0
Withholding tax									(1,831)	(216)	(2,578)
Transfer pricing									(2,481)	(11)	27
Change in valuation allowance									(5,255)	(11,718)	(924)
Other									(1,379)	2,957	(3,661)
Income tax benefit (expense)	$ 8,852	$ (1,451)	$ (4,506)	$ 3,407	$ (41,226)	$ 18,977	$ (3,904)	$ (334)	$ 6,302	$ (26,487)	$ (340)