Investments (Aggregate Carrying And Approximate Market Values Of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Total	$ 1,572,696	$ 1,673,864
Gross Unrealized Gains	6	645
Gross Unrealized Losses	214,483	168,989
Estimated Fair Value	1,358,219	1,505,520
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Total	230,270	292,293
Gross Unrealized Gains	3	346
Gross Unrealized Losses	29,825	24,324
Estimated Fair Value	200,448	268,315
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Total	1,302,747	1,342,666
Gross Unrealized Gains	3	299
Gross Unrealized Losses	181,147	140,686
Estimated Fair Value	1,121,603	1,202,279
Private label
Debt Securities, Available-for-sale [Line Items]
Total	7,035	7,695
Gross Unrealized Gains	0	0
Gross Unrealized Losses	490	464
Estimated Fair Value	6,545	7,231
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Total	4,597	4,590
Gross Unrealized Gains	0	0
Gross Unrealized Losses	290	762
Estimated Fair Value	4,307	3,828
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Total	28,047	26,620
Gross Unrealized Gains	0	0
Gross Unrealized Losses	2,731	2,753
Estimated Fair Value	$ 25,316	$ 23,867