Derivative Instruments (Consolidated Balance Sheets And Fair Value Of The Principal Derivative Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Other Assets
Derivative Assets
Gross Amounts of Recognized Assets	$ 3,585	$ 4,208
Gross Amounts Offset in the Balance Sheet	1,358	1,705
Net Amounts of Assets Presented in the Balance Sheet	2,227	2,503
Collateral	0	0
Net Amount	2,227	2,503
Other Assets | Interest Rate Futures
Derivative Assets
Gross Amounts of Recognized Assets	1,011	1,384
Gross Amounts Offset in the Balance Sheet	939	1,235
Net Amounts of Assets Presented in the Balance Sheet	72	149
Collateral	0	0
Net Amount	72	149
Other Assets | Foreign Currency Forward Contracts, Underwriting and Non-investment Operations
Derivative Assets
Gross Amounts of Recognized Assets	607	774
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	607	774
Collateral	0	0
Net Amount	607	774
Other Assets | Foreign Currency Forward Contracts, Investment Operations
Derivative Assets
Gross Amounts of Recognized Assets	560	621
Gross Amounts Offset in the Balance Sheet	403	447
Net Amounts of Assets Presented in the Balance Sheet	157	174
Collateral	0	0
Net Amount	157	174
Other Assets | Credit Default Swaps
Derivative Assets
Gross Amounts of Recognized Assets	1,407	1,429
Gross Amounts Offset in the Balance Sheet	16	23
Net Amounts of Assets Presented in the Balance Sheet	1,391	1,406
Collateral	0	0
Net Amount	1,391	1,406
Other Liabilities
Derivative Liabilities
Gross Amounts of Recognized Liabilities	5,505	13,527
Gross Amounts Offset in the Balance Sheet	1,526	2,102
Net Amounts of Liabilities Presented in the Balance Sheet	3,979	11,425
Collateral Pledged	125	789
Net Amount	3,854	10,636
Other Liabilities | Interest Rate Futures
Derivative Liabilities
Gross Amounts of Recognized Liabilities	1,064	2,030
Gross Amounts Offset in the Balance Sheet	939	1,235
Net Amounts of Liabilities Presented in the Balance Sheet	125	795
Collateral Pledged	125	789
Net Amount	0	6
Other Liabilities | Foreign Currency Forward Contracts, Underwriting and Non-investment Operations
Derivative Liabilities
Gross Amounts of Recognized Liabilities	3,203	10,550
Gross Amounts Offset in the Balance Sheet	168	397
Net Amounts of Liabilities Presented in the Balance Sheet	3,035	10,153
Collateral Pledged	0	0
Net Amount	3,035	10,153
Other Liabilities | Foreign Currency Forward Contracts, Investment Operations
Derivative Liabilities
Gross Amounts of Recognized Liabilities	952	766
Gross Amounts Offset in the Balance Sheet	403	447
Net Amounts of Liabilities Presented in the Balance Sheet	549	319
Collateral Pledged	0	0
Net Amount	549	319
Other Liabilities | Credit Default Swaps
Derivative Liabilities
Gross Amounts of Recognized Liabilities	286	181
Gross Amounts Offset in the Balance Sheet	16	23
Net Amounts of Liabilities Presented in the Balance Sheet	270	158
Collateral Pledged	0	0
Net Amount	$ 270	$ 158