Investments (Aggregate Carrying And Approximate Market Values Of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Total	$ 1,347,497	$ 1,128,163
Gross Unrealized Gains	30,578	49,336
Gross Unrealized Losses	5,998	702
Estimated Fair Value	1,372,077	1,176,797
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Total	267,923	266,483
Gross Unrealized Gains	7,750	11,467
Gross Unrealized Losses	589	139
Estimated Fair Value	275,084	277,811
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Total	1,038,806	815,682
Gross Unrealized Gains	20,906	34,807
Gross Unrealized Losses	5,289	105
Estimated Fair Value	1,054,423	850,384
Private label
Debt Securities, Available-for-sale [Line Items]
Total	8,864	9,976
Gross Unrealized Gains	701	916
Gross Unrealized Losses	0	0
Estimated Fair Value	9,565	10,892
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Total	4,567	4,557
Gross Unrealized Gains	0	0
Gross Unrealized Losses	118	457
Estimated Fair Value	4,449	4,100
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Total	27,337	31,465
Gross Unrealized Gains	1,221	2,146
Gross Unrealized Losses	2	1
Estimated Fair Value	$ 28,556	$ 33,610