Investment Securities Available for Sale (Schedule Of Unrealized Loss On Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	$ 1,128,609	$ 1,995,846
Less than 12 Months, Unrealized Losses	29,532	20,560
12 Months or Longer, Fair Value	2,660,551	1,445,859
12 Months or Longer, Unrealized Losses	131,719	36,717
Total Fair Value, Fair Value	3,789,160	3,441,705
Total Fair Value, Unrealized Losses	161,251	57,277
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	38,352	34,243
Less than 12 Months, Unrealized Losses	739	443
12 Months or Longer, Fair Value	62,905	29,562
12 Months or Longer, Unrealized Losses	1,887	491
Total Fair Value, Fair Value	101,257	63,805
Total Fair Value, Unrealized Losses	2,626	934
U.S. Government agency securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	29,727
Less than 12 Months, Unrealized Losses	258
12 Months or Longer, Fair Value	0
12 Months or Longer, Unrealized Losses	0
Total Fair Value, Fair Value	29,727
Total Fair Value, Unrealized Losses	258
Mortgage-backed securities issued by U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	15,655	36,810
Less than 12 Months, Unrealized Losses	364	357
12 Months or Longer, Fair Value	73,555	55,740
12 Months or Longer, Unrealized Losses	3,761	1,005
Total Fair Value, Fair Value	89,210	92,550
Total Fair Value, Unrealized Losses	4,125	1,362
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	830,455	1,271,012
Less than 12 Months, Unrealized Losses	24,765	10,263
12 Months or Longer, Fair Value	1,618,843	929,223
12 Months or Longer, Unrealized Losses	78,767	21,091
Total Fair Value, Fair Value	2,449,298	2,200,235
Total Fair Value, Unrealized Losses	103,532	31,354
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	214,420	653,781
Less than 12 Months, Unrealized Losses	3,406	9,497
12 Months or Longer, Fair Value	903,283	426,237
12 Months or Longer, Unrealized Losses	47,269	13,907
Total Fair Value, Fair Value	1,117,703	1,080,018
Total Fair Value, Unrealized Losses	50,675	23,404
Corporate debt and other debt securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Longer, Fair Value	1,965	5,097
12 Months or Longer, Unrealized Losses	35	223
Total Fair Value, Fair Value	1,965	5,097
Total Fair Value, Unrealized Losses	$ 35	$ 223