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	3 Months Ended
	Mar. 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	$ (20,610)
Available-for-sale Securities, Estimated fair value, Less than 12 months	1,087,259
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(17,931)
Available-for-sale Securities, Estimated fair value, 12 months or more	477,651
Available-for-sale Securities, Gross unrealized losses, Total	(38,541)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,564,910
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(3,399)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	474,593
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(30,505)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	698,117
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(33,904)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,172,710
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	(56)
Available-for-sale Securities, Estimated fair value, Less than 12 months	5,026
Available-for-sale Securities, Gross unrealized losses, Total	(56)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	5,026
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	(120)
Available-for-sale Securities, Estimated fair value, Less than 12 months	2,732
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(4,142)
Available-for-sale Securities, Estimated fair value, 12 months or more	67,133
Available-for-sale Securities, Gross unrealized losses, Total	(4,262)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	69,865
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	(16,980)
Available-for-sale Securities, Estimated fair value, Less than 12 months	885,475
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(6,326)
Available-for-sale Securities, Estimated fair value, 12 months or more	182,272
Available-for-sale Securities, Gross unrealized losses, Total	(23,306)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	1,067,747
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	(1,147)
Available-for-sale Securities, Estimated fair value, Less than 12 months	91,881
Available-for-sale Securities, Gross unrealized losses, Total	(1,147)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	91,881
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(451)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	181,393
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(2,347)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	42,425
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(2,798)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	223,818
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	(2,307)
Available-for-sale Securities, Estimated fair value, Less than 12 months	102,145
Available-for-sale Securities, Gross unrealized losses, 12 months or more	(2,637)
Available-for-sale Securities, Estimated fair value, 12 months or more	159,001
Available-for-sale Securities, Gross unrealized losses, Total	(4,944)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	261,146
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	(2,948)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	293,200
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	(28,158)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	655,692
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss, Total	(31,106)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total	948,892
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	(4,826)
Available-for-sale Securities, Estimated fair value, 12 months or more	69,245
Available-for-sale Securities, Gross unrealized losses, Total	(4,826)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 69,245