Investment Securities (Schedule Of Fair Value And Unrealized Losses Of Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months	$ 90,992	$ 392,066
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months Accumulated Loss	1,148	6,232
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,145,356	2,070,893
Debt Securities, Available-for-sale, Continuous Loss Position, 12 Months or Longer, Accumulated Loss	47,074	68,922
Debt Securities, Available-for-sale securities, Unrealized Loss Position	2,236,348	2,462,959
Debt Securities, Available-for-sale, Unrealized loss Position, Accumulated Loss	48,222	75,154
U.S. Treasury and agencies
Investment Holdings [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	19,789	39,656
Debt Securities, Available-for-sale, Continuous Loss Position, 12 Months or Longer, Accumulated Loss	209	346
Debt Securities, Available-for-sale securities, Unrealized Loss Position	19,789	39,656
Debt Securities, Available-for-sale, Unrealized loss Position, Accumulated Loss	209	346
Obligations of states and political subdivisions
Investment Holdings [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months	0	59,963
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months Accumulated Loss	0	800
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	35,434	38,691
Debt Securities, Available-for-sale, Continuous Loss Position, 12 Months or Longer, Accumulated Loss	671	1,786
Debt Securities, Available-for-sale securities, Unrealized Loss Position	35,434	98,654
Debt Securities, Available-for-sale, Unrealized loss Position, Accumulated Loss	671	2,586
Residential mortgage-backed securities and collateralized mortgage obligations
Investment Holdings [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months	90,992	332,103
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months Accumulated Loss	1,148	5,432
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,090,133	1,992,546
Debt Securities, Available-for-sale, Continuous Loss Position, 12 Months or Longer, Accumulated Loss	46,194	66,790
Debt Securities, Available-for-sale securities, Unrealized Loss Position	2,181,125	2,324,649
Debt Securities, Available-for-sale, Unrealized loss Position, Accumulated Loss	$ 47,342	$ 72,222