Investment Securities (Schedule Of Unrealized Loss On Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 2,984,023	$ 3,012,769
Less than 12 Months, Unrealized Losses	52,749	60,156
12 Months or Longer, Fair Value	32,179	33,315
12 Months or Longer, Unrealized Losses	1,308	1,381
Total Fair Value, Fair Value	3,016,202	3,046,084
Total Fair Value, Unrealized Losses	54,057	61,537
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	64,134	64,023
Less than 12 Months, Unrealized Losses	550	644
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value, Fair Value	64,134	64,023
Total Fair Value, Unrealized Losses	550	644
Mortgage-Backed Securities Issued By U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	123,299	128,121
Less than 12 Months, Unrealized Losses	1,185	1,240
12 Months or Longer, Fair Value	3,497	3,626
12 Months or Longer, Unrealized Losses	117	114
Total Fair Value, Fair Value	126,796	131,747
Total Fair Value, Unrealized Losses	1,302	1,354
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,155,464	2,123,181
Less than 12 Months, Unrealized Losses	38,594	42,571
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value, Fair Value	2,155,464	2,123,181
Total Fair Value, Unrealized Losses	38,594	42,571
Collateralized Mortgage Obligations Issued By U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	641,126	682,492
Less than 12 Months, Unrealized Losses	12,420	15,653
12 Months or Longer, Fair Value	23,723	24,801
12 Months or Longer, Unrealized Losses	888	908
Total Fair Value, Fair Value	664,849	707,293
Total Fair Value, Unrealized Losses	13,308	16,561
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	14,952
Less than 12 Months, Unrealized Losses	0	48
12 Months or Longer, Fair Value	4,959	4,888
12 Months or Longer, Unrealized Losses	303	359
Total Fair Value, Fair Value	4,959	19,840
Total Fair Value, Unrealized Losses	$ 303	$ 407