Income Tax (Tax Effects of Temporary Differences that Give Rise to Significant Portions of the Deferred Income Tax Asset and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets, Net [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals	$ 86,092	$ 80,905
Deferred Tax Assets Reinsurance Transactions	102,014	96,043
Deferred Tax Assets Cash And Invested Assets	28,398	557
Deferred Tax Assets Investment Income	80,200	43,230
Deferred Tax Assets Deferred Acquisition Costs Capitalized For Tax	124,707	88,531
Deferred Tax Assets, Operating Loss Carryforwards	405,958	535,374
Deferred Tax Assets Deferred Acquisition Costs Capitalized For Financial Reporting	32,897	102,143
Deferred Tax Assets, Gross	860,266	946,783
Deferred Tax Assets, Valuation Allowance	(181,110)	(226,884)
Deferred Tax Assets, Net	679,156	719,899
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost	843,328	627,378
Deferred Tax Liabilities Reinsurance Transactions	1,151,419	1,547,101
Deferred Tax Liabilities Cash And Invested Assets	345,836	674,569
Deferred Tax Liabilities Investment Income	9,493	1,858
Deferred Tax Liabilities, Unrealized Currency Transaction Gains	52,928	33,803
Deferred Tax Liabilities, Prepaid Expenses	25,433	0
Total Deferred Income Tax Liabilities	2,428,437	2,884,709
Deferred Tax Liabilities, Net	1,749,281	2,164,810
Balance Sheet Presentation Of Deferred Tax Liabilities [Abstract]
Deferred Tax Assets, Other	49,519	33,499
Deferred income taxes	1,798,800	2,198,309
Deferred Tax Liabilities, Net	$ 1,749,281	$ 2,164,810