Derivative Instruments (Consolidated Balance Sheets And Fair Value Of The Principal Derivative Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Other Assets
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	$ 4,208	$ 6,968
Gross Amounts Offset in the Balance Sheet	1,705	1,662
Net Amounts of Assets Presented in the Balance Sheet	2,503	5,306
Collateral	0	0
Net Amount	2,503	5,306
Other Assets | Interest Rate Futures
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	1,384	1,059
Gross Amounts Offset in the Balance Sheet	1,235	937
Net Amounts of Assets Presented in the Balance Sheet	149	122
Collateral	0	0
Net Amount	149	122
Other Assets | Foreign Currency Forward Contracts, Underwriting and Non-investment Operations
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	774	4,645
Gross Amounts Offset in the Balance Sheet	0	82
Net Amounts of Assets Presented in the Balance Sheet	774	4,563
Collateral	0	0
Net Amount	774	4,563
Other Assets | Foreign Currency Forward Contracts, Investment Operations
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	621	1,007
Gross Amounts Offset in the Balance Sheet	447	599
Net Amounts of Assets Presented in the Balance Sheet	174	408
Collateral	0	0
Net Amount	174	408
Other Assets | Credit Default Swaps
Derivative Assets [Abstract]
Gross Amounts of Recognized Assets	1,429	257
Gross Amounts Offset in the Balance Sheet	23	44
Net Amounts of Assets Presented in the Balance Sheet	1,406	213
Collateral	0	0
Net Amount	1,406	213
Other Liabilities
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	13,527	5,481
Gross Amounts Offset in the Balance Sheet	2,102	1,661
Net Amounts of Liabilities Presented in the Balance Sheet	11,425	3,820
Collateral Pledged	789	1,803
Net Amount	10,636	2,017
Other Liabilities | Interest Rate Futures
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	2,030	2,293
Gross Amounts Offset in the Balance Sheet	1,235	937
Net Amounts of Liabilities Presented in the Balance Sheet	795	1,356
Collateral Pledged	789	1,356
Net Amount	6	0
Other Liabilities | Foreign Currency Forward Contracts, Underwriting and Non-investment Operations
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	10,550	1,891
Gross Amounts Offset in the Balance Sheet	397	81
Net Amounts of Liabilities Presented in the Balance Sheet	10,153	1,810
Collateral Pledged	0	0
Net Amount	10,153	1,810
Other Liabilities | Foreign Currency Forward Contracts, Investment Operations
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	766	806
Gross Amounts Offset in the Balance Sheet	447	599
Net Amounts of Liabilities Presented in the Balance Sheet	319	207
Collateral Pledged	0	0
Net Amount	319	207
Other Liabilities | Credit Default Swaps
Derivative Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	181	491
Gross Amounts Offset in the Balance Sheet	23	44
Net Amounts of Liabilities Presented in the Balance Sheet	158	447
Collateral Pledged	0	447
Net Amount	$ 158	$ 0