The portion of earnings or loss from continuing operations before income taxes that is attributable to domestic operations.

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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The portion of earnings or loss from continuing operations before income taxes that is attributable to foreign operations, which is defined as Income or Loss generated from operations located outside the entity's country of domicile.

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Taxation (Income Before Income Taxes, Foreign and Domestic) (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 Expense (Benefit)
Income (loss) before taxes	$ (132,838)	$ 50,280	$ 256,373	$ 88,800	$ 43,425	$ (722,471)	$ 218,254	$ 132,608	$ 262,615	$ (328,184)	$ 630,388
Bermuda
Income Tax Expense (Benefit)
Domestic									349,959	(262,827)	652,758
U.S.
Income Tax Expense (Benefit)
Foreign									(56,261)	(11,897)	(1,236)
U.K.
Income Tax Expense (Benefit)
Foreign									(28,574)	(41,656)	(24,278)
Singapore
Income Tax Expense (Benefit)
Foreign									(3,226)	(12,421)	2,180
Ireland
Income Tax Expense (Benefit)
Foreign									551	617	964
Switzerland
Income Tax Expense (Benefit)
Foreign									$ 166	$ 0	$ 0