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	Jun. 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	$ (28,185)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,213,244
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(19,451)
Available-for-sale Securities, Estimated fair value, 12 months or more	474,838
Available-for-sale Securities, Gross unrealized losses, Total	(47,636)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,688,082
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(13,664)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,553,905
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(34,182)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	659,774
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(47,846)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	2,213,679
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	(58)
Available-for-sale Securities, Estimated fair value, Less than 12 months	4,811
Available-for-sale Securities, Gross unrealized losses, Total	(58)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	4,811
State And Municipal 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	(2)
Available-for-sale Securities, Estimated fair value, Less than 12 months	354
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(4,206)
Available-for-sale Securities, Estimated fair value, 12 months or more	69,107
Available-for-sale Securities, Gross unrealized losses, Total	(4,208)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	69,461
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	(20,942)
Available-for-sale Securities, Estimated fair value, Less than 12 months	775,896
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(7,100)
Available-for-sale Securities, Estimated fair value, 12 months or more	181,077
Available-for-sale Securities, Gross unrealized losses, Total	(28,042)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	956,973
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	(4,855)
Available-for-sale Securities, Estimated fair value, Less than 12 months	348,972
Available-for-sale Securities, Gross unrealized losses, Total	(4,855)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	348,972
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(5,962)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,007,827
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(2,358)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	37,121
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(8,320)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,044,948
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	(2,328)
Available-for-sale Securities, Estimated fair value, Less than 12 months	83,211
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(2,634)
Available-for-sale Securities, Estimated fair value, 12 months or more	156,268
Available-for-sale Securities, Gross unrealized losses, Total	(4,962)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	239,479
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(7,590)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	488,456
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(31,824)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	622,653
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(39,414)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,111,109
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	(5,511)
Available-for-sale Securities, Estimated fair value, 12 months or more	68,386
Available-for-sale Securities, Gross unrealized losses, Total	(5,511)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	68,386
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(112)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	57,622
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(112)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 57,622