Investment Securities (Schedule Of Fair Value And Unrealized Losses Of Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 3,843	$ 606,646
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	10	5,982
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	23,493	404,708
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	312	4,065
Available-for-sale securities, Unrealized Loss Position, Fair Value	27,336	1,011,354
Available-for-sale, Unrealized loss Position, Unrealized Losses	322	10,047
U.S. Treasury and agencies
Investment Holdings [Line Items]
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value		313,169
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses		4,324
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value		0
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses		0
Available-for-sale securities, Unrealized Loss Position, Fair Value		313,169
Available-for-sale, Unrealized loss Position, Unrealized Losses		4,324
Obligations of states and political subdivisions
Investment Holdings [Line Items]
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	3,843	4,611
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	10	30
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	774	1,906
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	5	7
Available-for-sale securities, Unrealized Loss Position, Fair Value	4,617	6,517
Available-for-sale, Unrealized loss Position, Unrealized Losses	15	37
Residential mortgage-backed securities and collateralized mortgage obligations
Investment Holdings [Line Items]
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	288,866
Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	0	1,628
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	22,719	402,802
Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	307	4,058
Available-for-sale securities, Unrealized Loss Position, Fair Value	22,719	691,668
Available-for-sale, Unrealized loss Position, Unrealized Losses	$ 307	$ 5,686