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	Mar. 31, 2019 USD ($)
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Gross unrealized losses, Less than 12 months	$ (13,951)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,382,566
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(9,920)
Available-for-sale Securities, Estimated fair value, 12 months or more	659,717
Available-for-sale Securities, Gross unrealized losses, Total	(23,871)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	2,042,283
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(31,916)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,229,947
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(23,280)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	872,189
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(55,196)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	3,102,136
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	(22)
Available-for-sale Securities, Estimated fair value, Less than 12 months	3,173
Available-for-sale Securities, Gross unrealized losses, Total	(22)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	3,173
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	(28)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,146
Available-for-sale Securities, Gross unrealized losses, Total	(28)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,146
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	(106)
Available-for-sale Securities, Estimated fair value, Less than 12 months	104,241
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(5,310)
Available-for-sale Securities, Estimated fair value, 12 months or more	505,628
Available-for-sale Securities, Gross unrealized losses, Total	(5,416)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	609,869
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	(13,794)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,273,856
Available-for-sale Securities, Gross unrealized losses, Total	(13,794)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,273,856
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(31,877)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,111,245
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(6,973)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	229,646
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(38,850)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	2,340,891
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	(1)
Available-for-sale Securities, Estimated fair value, Less than 12 months	150
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(1,866)
Available-for-sale Securities, Estimated fair value, 12 months or more	83,461
Available-for-sale Securities, Gross unrealized losses, Total	(1,867)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	83,611
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(39)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	118,702
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(16,307)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	642,543
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(16,346)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	761,245
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	(2,744)
Available-for-sale Securities, Estimated fair value, 12 months or more	70,628
Available-for-sale Securities, Gross unrealized losses, Total	(2,744)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 70,628