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	Sep. 30, 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	$ (22,667)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,129,854
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(26,542)
Available-for-sale Securities, Estimated fair value, 12 months or more	634,783
Available-for-sale Securities, Gross unrealized losses, Total	(49,209)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,764,637
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(24,445)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,287,199
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(39,563)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	681,802
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(64,008)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	2,969,001
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	(61)
Available-for-sale Securities, Estimated fair value, Less than 12 months	5,040
Available-for-sale Securities, Gross unrealized losses, Total	(61)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	5,040
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	(4,377)
Available-for-sale Securities, Estimated fair value, 12 months or more	68,481
Available-for-sale Securities, Gross unrealized losses, Total	(4,377)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	68,481
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	(14,053)
Available-for-sale Securities, Estimated fair value, Less than 12 months	565,671
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(11,672)
Available-for-sale Securities, Estimated fair value, 12 months or more	310,351
Available-for-sale Securities, Gross unrealized losses, Total	(25,725)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	876,022
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	(7,810)
Available-for-sale Securities, Estimated fair value, Less than 12 months	517,276
Available-for-sale Securities, Gross unrealized losses, Total	(7,810)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	517,276
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(12,298)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,675,810
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(2,460)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	42,507
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(14,758)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,718,317
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	(731)
Available-for-sale Securities, Estimated fair value, Less than 12 months	40,606
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(4,610)
Available-for-sale Securities, Estimated fair value, 12 months or more	188,110
Available-for-sale Securities, Gross unrealized losses, Total	(5,341)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	228,716
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(11,804)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	556,381
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(37,103)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	639,295
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(48,907)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,195,676
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	(5,883)
Available-for-sale Securities, Estimated fair value, 12 months or more	67,841
Available-for-sale Securities, Gross unrealized losses, Total	(5,883)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	67,841
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(343)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	55,008
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(343)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	55,008
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	(12)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,261
Available-for-sale Securities, Gross unrealized losses, Total	(12)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 1,261

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