Available-For-Sale And Held-To-Maturity Securities (Schedule Of Gross Unrealized Losses And The Estimated Fair Value By Length Of Time In A Loss Position) (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, Less than 12 months	$ (21,974)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,721,361
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(33,930)
Available-for-sale Securities, Estimated fair value, 12 months or more	905,325
Available-for-sale Securities, Gross unrealized losses, Total	(55,904)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	2,626,686
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(71,819)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,890,127
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(30,205)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	757,661
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(102,024)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	3,647,788
U.S. Government Agency Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, Less than 12 months	(35)
Available-for-sale Securities, Estimated fair value, Less than 12 months	3,752
Available-for-sale Securities, Gross unrealized losses, Total	(35)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	3,752
State And Municipal Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(4,261)
Available-for-sale Securities, Estimated fair value, 12 months or more	68,146
Available-for-sale Securities, Gross unrealized losses, Total	(4,261)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	68,146
Asset-Backed Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, Less than 12 months	(16,108)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,348,927
Available-for-sale Securities, Gross unrealized losses, Total	(16,108)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,348,927
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(68,308)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,579,117
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(2,027)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	42,712
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(70,335)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	2,621,829
Mortgage Backed Securities [Member] \| Agency [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, Less than 12 months	(186)
Available-for-sale Securities, Estimated fair value, Less than 12 months	16,124
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(3,786)
Available-for-sale Securities, Estimated fair value, 12 months or more	188,069
Available-for-sale Securities, Gross unrealized losses, Total	(3,972)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	204,193
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(3,511)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	311,010
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(28,178)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	714,949
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(31,689)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,025,959
Mortgage Backed Securities [Member] \| Commercial [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(4,700)
Available-for-sale Securities, Estimated fair value, 12 months or more	68,850
Available-for-sale Securities, Gross unrealized losses, Total	(4,700)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	68,850
Mortgage Backed Securities [Member] \| Non-Agency [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, Less than 12 months	(26)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,214
Available-for-sale Securities, Gross unrealized losses, Total	(26)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,214
Mortgage Backed Securities [Member] \| Corporate Fixed Income Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, Less than 12 months	(5,619)
Available-for-sale Securities, Estimated fair value, Less than 12 months	351,344
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(21,183)
Available-for-sale Securities, Estimated fair value, 12 months or more	580,260
Available-for-sale Securities, Gross unrealized losses, Total	(26,802)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 931,604

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