Derivative Instruments (Consolidated Balance Sheets And Fair Value Of The Principal Derivative Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Other assets
Derivative Assets
Gross Amounts of Recognized Assets	$ 7,048	$ 4,208
Gross Amounts Offset in the Balance Sheet	1,770	1,705
Net Amounts of Assets Presented in the Balance Sheet	5,278	2,503
Collateral	0	0
Net Amount	5,278	2,503
Other assets | Interest rate futures
Derivative Assets
Gross Amounts of Recognized Assets	740	1,384
Gross Amounts Offset in the Balance Sheet	614	1,235
Net Amounts of Assets Presented in the Balance Sheet	126	149
Collateral	0	0
Net Amount	126	149
Other assets | Interest rate swaps
Derivative Assets
Gross Amounts of Recognized Assets	551
Gross Amounts Offset in the Balance Sheet	277
Net Amounts of Assets Presented in the Balance Sheet	274
Collateral	0
Net Amount	274
Other assets | Foreign Currency Forward Contracts, Underwriting and Non-investment Operations
Derivative Assets
Gross Amounts of Recognized Assets	4,758	774
Gross Amounts Offset in the Balance Sheet	557	0
Net Amounts of Assets Presented in the Balance Sheet	4,201	774
Collateral	0	0
Net Amount	4,201	774
Other assets | Foreign Currency Forward Contracts, Investment Operations
Derivative Assets
Gross Amounts of Recognized Assets	43	621
Gross Amounts Offset in the Balance Sheet	14	447
Net Amounts of Assets Presented in the Balance Sheet	29	174
Collateral	0	0
Net Amount	29	174
Other assets | Credit default swaps
Derivative Assets
Gross Amounts of Recognized Assets	956	1,429
Gross Amounts Offset in the Balance Sheet	308	23
Net Amounts of Assets Presented in the Balance Sheet	648	1,406
Collateral	0	0
Net Amount	648	1,406
Other liabilities
Derivative Liabilities
Gross Amounts of Recognized Liabilities	4,547	13,527
Gross Amounts Offset in the Balance Sheet	1,213	2,102
Net Amounts of Liabilities Presented in the Balance Sheet	3,334	11,425
Collateral Pledged	243	789
Net Amount	3,091	10,636
Other liabilities | Interest rate futures
Derivative Liabilities
Gross Amounts of Recognized Liabilities	854	2,030
Gross Amounts Offset in the Balance Sheet	614	1,235
Net Amounts of Liabilities Presented in the Balance Sheet	240	795
Collateral Pledged	240	789
Net Amount	0	6
Other liabilities | Interest rate swaps
Derivative Liabilities
Gross Amounts of Recognized Liabilities	280
Gross Amounts Offset in the Balance Sheet	277
Net Amounts of Liabilities Presented in the Balance Sheet	3
Collateral Pledged	3
Net Amount	0
Other liabilities | Foreign Currency Forward Contracts, Underwriting and Non-investment Operations
Derivative Liabilities
Gross Amounts of Recognized Liabilities	2,996	10,550
Gross Amounts Offset in the Balance Sheet	0	397
Net Amounts of Liabilities Presented in the Balance Sheet	2,996	10,153
Collateral Pledged	0	0
Net Amount	2,996	10,153
Other liabilities | Foreign Currency Forward Contracts, Investment Operations
Derivative Liabilities
Gross Amounts of Recognized Liabilities	90	766
Gross Amounts Offset in the Balance Sheet	14	447
Net Amounts of Liabilities Presented in the Balance Sheet	76	319
Collateral Pledged	0	0
Net Amount	76	319
Other liabilities | Credit default swaps
Derivative Liabilities
Gross Amounts of Recognized Liabilities	327	181
Gross Amounts Offset in the Balance Sheet	308	23
Net Amounts of Liabilities Presented in the Balance Sheet	19	158
Collateral Pledged	0	0
Net Amount	$ 19	$ 158