Investments (Aggregate Carrying And Approximate Market Values Of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Total	$ 1,604,706	$ 1,673,864
Gross Unrealized Gains	1,033	645
Gross Unrealized Losses	149,480	168,989
Estimated Fair Value	1,456,259	1,505,520
Certificates of deposit, at carrying value	500	700
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Total	247,589	292,293
Gross Unrealized Gains	487	346
Gross Unrealized Losses	19,202	24,324
Estimated Fair Value	228,874	268,315
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Total	1,318,398	1,342,666
Gross Unrealized Gains	546	299
Gross Unrealized Losses	126,984	140,686
Estimated Fair Value	1,191,960	1,202,279
Private label
Debt Securities, Available-for-sale [Line Items]
Total	7,554	7,695
Gross Unrealized Gains	0	0
Gross Unrealized Losses	401	464
Estimated Fair Value	7,153	7,231
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Total	4,592	4,590
Gross Unrealized Gains	0	0
Gross Unrealized Losses	467	762
Estimated Fair Value	4,125	3,828
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Total	26,573	26,620
Gross Unrealized Gains	0	0
Gross Unrealized Losses	2,426	2,753
Estimated Fair Value	$ 24,147	$ 23,867