Derivative Instruments (Consolidated Balance Sheets And Fair Value Of The Principal Derivative Instruments) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Other assets
Derivative Assets
Gross Amounts of Recognized Assets	$ 9,281	$ 6,530
Gross Amounts Offset in the Balance Sheet	410	893
Net Amounts of Assets Presented in the Balance Sheet	8,871	5,637
Collateral	0	0
Net Amount	8,871	5,637
Other assets | Interest rate futures
Derivative Assets
Gross Amounts of Recognized Assets	175	684
Gross Amounts Offset in the Balance Sheet	157	524
Net Amounts of Assets Presented in the Balance Sheet	18	160
Collateral	0	0
Net Amount	18	160
Other assets | Interest rate swaps
Derivative Assets
Gross Amounts of Recognized Assets	357	424
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	357	424
Collateral	0	0
Net Amount	357	424
Other assets | Foreign currency forward contracts, underwriting and non-investment operations
Derivative Assets
Gross Amounts of Recognized Assets	7,070	3,865
Gross Amounts Offset in the Balance Sheet	175	358
Net Amounts of Assets Presented in the Balance Sheet	6,895	3,507
Collateral	0	0
Net Amount	6,895	3,507
Other assets | Foreign currency forward contracts, investment operations
Derivative Assets
Gross Amounts of Recognized Assets	79	39
Gross Amounts Offset in the Balance Sheet	78	11
Net Amounts of Assets Presented in the Balance Sheet	1	28
Collateral	0	0
Net Amount	1	28
Other assets | Credit default swaps
Derivative Assets
Gross Amounts of Recognized Assets	1,600	1,518
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Assets Presented in the Balance Sheet	1,600	1,518
Collateral	0	0
Net Amount	1,600	1,518
Other liabilities
Derivative Liabilities
Gross Amounts of Recognized Liabilities	1,592	1,536
Gross Amounts Offset in the Balance Sheet	235	535
Net Amounts of Liabilities Presented in the Balance Sheet	1,357	1,001
Collateral Pledged	313	227
Net Amount	1,044	774
Other liabilities | Interest rate futures
Derivative Liabilities
Gross Amounts of Recognized Liabilities	404	729
Gross Amounts Offset in the Balance Sheet	157	524
Net Amounts of Liabilities Presented in the Balance Sheet	247	205
Collateral Pledged	247	205
Net Amount	0	0
Other liabilities | Interest rate swaps
Derivative Liabilities
Gross Amounts of Recognized Liabilities	53
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Liabilities Presented in the Balance Sheet	53
Collateral Pledged	53
Net Amount	0
Other liabilities | Foreign currency forward contracts, underwriting and non-investment operations
Derivative Liabilities
Gross Amounts of Recognized Liabilities	479	670
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Balance Sheet	479	670
Collateral Pledged	0	0
Net Amount	479	670
Other liabilities | Foreign currency forward contracts, investment operations
Derivative Liabilities
Gross Amounts of Recognized Liabilities	643	115
Gross Amounts Offset in the Balance Sheet	78	11
Net Amounts of Liabilities Presented in the Balance Sheet	565	104
Collateral Pledged	0	0
Net Amount	565	104
Other liabilities | Credit default swaps
Derivative Liabilities
Gross Amounts of Recognized Liabilities	13	22
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Balance Sheet	13	22
Collateral Pledged	13	22
Net Amount	$ 0	$ 0