Investments (Aggregate Carrying And Approximate Market Values Of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,109,274	$ 794,117
Gross Unrealized Gains	49,689	18,210
Gross Unrealized Losses	1,564	2,221
Estimated Fair Value	1,157,399	810,106
U.S Treasuries and U.S. Government Agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	500
Gross Unrealized Gains	0	2
Gross Unrealized Losses	0	0
Estimated Fair Value	0	502
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	255,677	112,393
Gross Unrealized Gains	8,369	4,800
Gross Unrealized Losses	744	6
Estimated Fair Value	263,302	117,187
Mortgage-backed securities: U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	804,912	631,637
Gross Unrealized Gains	38,459	12,292
Gross Unrealized Losses	138	1,825
Estimated Fair Value	843,233	642,104
Mortgage-backed securities: Private label
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,375	10,896
Gross Unrealized Gains	1,002	589
Gross Unrealized Losses	0	0
Estimated Fair Value	11,377	11,485
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,554	4,781
Gross Unrealized Gains	0	27
Gross Unrealized Losses	662	347
Estimated Fair Value	3,892	4,461
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,515	31,669
Gross Unrealized Gains	1,859	500
Gross Unrealized Losses	20	43
Estimated Fair Value	33,354	32,126
Total Debt Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,107,033	791,876
Gross Unrealized Gains	49,689	18,210
Gross Unrealized Losses	1,564	2,221
Estimated Fair Value	1,155,158	807,865
Certificates of deposit held for investment
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,241	2,241
Estimated Fair Value	$ 2,241	$ 2,241