Derivative Instruments (Schedule of Location on Consolidated Balance Sheets and Fair Value of Principal Derivative Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivative Assets
Gross Amounts of Recognized Assets	$ 28,154	$ 22,874
Gross Amounts Offset in the Balance Sheet	3,829	3,944
Net Amounts of Assets Presented in the Balance Sheet	24,325	18,930
Collateral	3,601	0
Net Amount	20,724	18,930
Derivative Liabilities
Gross Amounts of Recognized Liabilities	8,160	8,225
Gross Amounts Offset in the Balance Sheet	772	1,684
Net Amounts of Liabilities Presented in the Balance Sheet	7,388	6,540
Collateral Pledged	1,473	2,132
Net Amount	5,915	4,408
Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	28,090
Gross Amounts Offset in the Balance Sheet	3,162
Net Amounts of Assets Presented in the Balance Sheet	24,928
Collateral	3,601
Net Amount	21,327
Derivative Liabilities
Gross Amounts of Recognized Liabilities	6,342
Gross Amounts Offset in the Balance Sheet	772
Net Amounts of Liabilities Presented in the Balance Sheet	5,570
Collateral Pledged	1,473
Net Amount	4,097
Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	64
Gross Amounts Offset in the Balance Sheet	667
Net Amounts of Assets Presented in the Balance Sheet	(603)
Collateral	0
Net Amount	(603)
Other assets | Interest rate futures | Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	234	971
Gross Amounts Offset in the Balance Sheet	122	636
Net Amounts of Assets Presented in the Balance Sheet	112	335
Collateral	0	0
Net Amount	112	335
Other assets | Interest rate swaps | Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets		860
Gross Amounts Offset in the Balance Sheet		0
Net Amounts of Assets Presented in the Balance Sheet		860
Collateral		0
Net Amount		860
Other assets | Foreign currency forward contracts | Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	22,702	16,459
Gross Amounts Offset in the Balance Sheet	2,418	2,260
Net Amounts of Assets Presented in the Balance Sheet	20,284	14,199
Collateral	0	0
Net Amount	20,284	14,199
Other assets | Foreign currency forward contracts | Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	1,082	3,194
Gross Amounts Offset in the Balance Sheet	622	71
Net Amounts of Assets Presented in the Balance Sheet	460	3,123
Collateral	0	0
Net Amount	460	3,123
Other assets | Foreign currency forward contracts | Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	64
Gross Amounts Offset in the Balance Sheet	667
Net Amounts of Assets Presented in the Balance Sheet	(603)
Collateral	0
Net Amount	(603)
Other assets | Credit default swaps | Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	37
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Assets Presented in the Balance Sheet	37
Collateral	0
Net Amount	37
Other assets | Total return swaps | Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	3,744
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Assets Presented in the Balance Sheet	3,744
Collateral	3,601
Net Amount	143
Other assets | Equity futures | Not Designated as Hedging Instrument
Derivative Assets
Gross Amounts of Recognized Assets	291	1,390
Gross Amounts Offset in the Balance Sheet	0	977
Net Amounts of Assets Presented in the Balance Sheet	291	413
Collateral	0	0
Net Amount	291	413
Other liabilities | Interest rate futures | Not Designated as Hedging Instrument
Derivative Liabilities
Gross Amounts of Recognized Liabilities	1,545	910
Gross Amounts Offset in the Balance Sheet	122	636
Net Amounts of Liabilities Presented in the Balance Sheet	1,423	273
Collateral Pledged	1,423	273
Net Amount	0	0
Other liabilities | Interest rate swaps | Not Designated as Hedging Instrument
Derivative Liabilities
Gross Amounts of Recognized Liabilities	50	506
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Balance Sheet	50	506
Collateral Pledged	50	254
Net Amount	0	252
Other liabilities | Foreign currency forward contracts | Not Designated as Hedging Instrument
Derivative Liabilities
Gross Amounts of Recognized Liabilities	3,808	4,154
Gross Amounts Offset in the Balance Sheet	28	0
Net Amounts of Liabilities Presented in the Balance Sheet	3,780	4,154
Collateral Pledged	0	0
Net Amount	3,780	4,154
Other liabilities | Foreign currency forward contracts | Not Designated as Hedging Instrument
Derivative Liabilities
Gross Amounts of Recognized Liabilities	939	72
Gross Amounts Offset in the Balance Sheet	622	71
Net Amounts of Liabilities Presented in the Balance Sheet	317	1
Collateral Pledged	0	0
Net Amount	317	1
Other liabilities | Foreign currency forward contracts | Designated as Hedging Instrument
Derivative Liabilities
Gross Amounts of Recognized Liabilities	1,818
Gross Amounts Offset in the Balance Sheet	0
Net Amounts of Liabilities Presented in the Balance Sheet	1,818
Collateral Pledged	0
Net Amount	$ 1,818
Other liabilities | Credit default swaps | Not Designated as Hedging Instrument
Derivative Liabilities
Gross Amounts of Recognized Liabilities		1,606
Gross Amounts Offset in the Balance Sheet		0
Net Amounts of Liabilities Presented in the Balance Sheet		1,606
Collateral Pledged		1,605
Net Amount		1
Other liabilities | Equity futures | Not Designated as Hedging Instrument
Derivative Liabilities
Gross Amounts of Recognized Liabilities		977
Gross Amounts Offset in the Balance Sheet		977
Net Amounts of Liabilities Presented in the Balance Sheet		0
Collateral Pledged		0
Net Amount		$ 0