Investments (Aggregate Carrying And Approximate Market Values Of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,306,411	$ 1,130,155
Gross Unrealized Gains	37,044	49,336
Gross Unrealized Losses	2,774	702
Estimated Fair Value	1,340,681	1,178,789
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	271,658	266,483
Gross Unrealized Gains	9,853	11,467
Gross Unrealized Losses	167	139
Estimated Fair Value	281,344	277,811
Mortgage-backed securities: U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	987,297	815,682
Gross Unrealized Gains	24,937	34,807
Gross Unrealized Losses	2,327	105
Estimated Fair Value	1,009,907	850,384
Mortgage-backed securities: Private label
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,271	9,976
Gross Unrealized Gains	786	916
Gross Unrealized Losses	0	0
Estimated Fair Value	10,057	10,892
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,563	4,557
Gross Unrealized Gains	0	0
Gross Unrealized Losses	280	457
Estimated Fair Value	4,283	4,100
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	32,377	31,465
Gross Unrealized Gains	1,468	2,146
Gross Unrealized Losses	0	1
Estimated Fair Value	33,845	33,610
Total Debt Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,305,166	1,128,163
Gross Unrealized Gains	37,044	49,336
Gross Unrealized Losses	2,774	702
Estimated Fair Value	1,339,436	1,176,797
Certificates of deposit held for investment
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,245	1,992
Estimated Fair Value	$ 1,245	$ 1,992