Investments (Aggregate Carrying And Approximate Market Values Of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 889,940	$ 794,117
Gross Unrealized Gains	46,950	18,210
Gross Unrealized Losses	2,777	2,221
Estimated Fair Value	934,113	810,106
U.S Treasuries and U.S. Government Agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	500	500
Gross Unrealized Gains	2	2
Gross Unrealized Losses	0	0
Estimated Fair Value	502	502
Obligations Of States And Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	121,684	112,393
Gross Unrealized Gains	4,896	4,800
Gross Unrealized Losses	630	6
Estimated Fair Value	125,950	117,187
U.S. Government Agencies Mortgage-backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	718,679	631,637
Gross Unrealized Gains	41,318	12,292
Gross Unrealized Losses	532	1,825
Estimated Fair Value	759,465	642,104
Private Label
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,669	10,896
Gross Unrealized Gains	269	589
Gross Unrealized Losses	76	0
Estimated Fair Value	10,862	11,485
Trust Preferred Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,549	4,781
Gross Unrealized Gains	0	27
Gross Unrealized Losses	1,149	347
Estimated Fair Value	3,400	4,461
Corporate Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,618	31,669
Gross Unrealized Gains	465	500
Gross Unrealized Losses	390	43
Estimated Fair Value	31,693	32,126
Debt Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	887,699	791,876
Gross Unrealized Gains	46,950	18,210
Gross Unrealized Losses	2,777	2,221
Estimated Fair Value	931,872	807,865
Certificates of Deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,241	2,241
Estimated Fair Value	$ 2,241	$ 2,241