Derivative Instruments (Consolidated Balance Sheets And Fair Value Of The Principal Derivative Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Assets
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	$ 6,530	$ 4,208
Gross Amounts Offset in the Balance Sheet	893	1,705
Net Amounts of Assets Presented in the Balance Sheet	5,637	2,503
Collateral	0	0
Net Amount	5,637	2,503
Other Assets | Interest rate futures
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	684	1,384
Gross Amounts Offset in the Balance Sheet	524	1,235
Net Amounts of Assets Presented in the Balance Sheet	160	149
Collateral	0	0
Net Amount	160	149
Other Assets | Interest rate swaps
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	424
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Assets Presented in the Balance Sheet	424
Collateral	0
Net Amount	424
Other Assets | Foreign currency forward contracts, underwriting and non-investment operations
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	3,865	774
Gross Amounts Offset in the Balance Sheet	358	0
Net Amounts of Assets Presented in the Balance Sheet	3,507	774
Collateral	0	0
Net Amount	3,507	774
Other Assets | Foreign currency forward contracts, investment operations
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	39	621
Gross Amounts Offset in the Balance Sheet	11	447
Net Amounts of Assets Presented in the Balance Sheet	28	174
Collateral	0	0
Net Amount	28	174
Other Assets | Credit default swaps
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	1,518	1,429
Gross Amounts Offset in the Balance Sheet	0	23
Net Amounts of Assets Presented in the Balance Sheet	1,518	1,406
Collateral	0	0
Net Amount	1,518	1,406
Other Liabilities
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	1,536	13,527
Gross Amounts Offset in the Balance Sheet	535	2,102
Net Amounts of Liabilities Presented in the Balance Sheet	1,001	11,425
Collateral Pledged	227	789
Net Amount	774	10,636
Other Liabilities | Interest rate futures
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	729	2,030
Gross Amounts Offset in the Balance Sheet	524	1,235
Net Amounts of Liabilities Presented in the Balance Sheet	205	795
Collateral Pledged	205	789
Net Amount	0	6
Other Liabilities | Foreign currency forward contracts, underwriting and non-investment operations
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	670	10,550
Gross Amounts Offset in the Balance Sheet	0	397
Net Amounts of Liabilities Presented in the Balance Sheet	670	10,153
Collateral Pledged	0	0
Net Amount	670	10,153
Other Liabilities | Foreign currency forward contracts, investment operations
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	115	766
Gross Amounts Offset in the Balance Sheet	11	447
Net Amounts of Liabilities Presented in the Balance Sheet	104	319
Collateral Pledged	0	0
Net Amount	104	319
Other Liabilities | Credit default swaps
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	22	181
Gross Amounts Offset in the Balance Sheet	0	23
Net Amounts of Liabilities Presented in the Balance Sheet	22	158
Collateral Pledged	22	0
Net Amount	$ 0	$ 158