Investment Securities Available for Sale (Schedule Of Unrealized Loss On Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 1,995,846	$ 3,012,769
Less than 12 Months, Unrealized Losses	20,560	60,156
12 Months or Longer, Fair Value	1,445,859	33,315
12 Months or Longer, Unrealized Losses	36,717	1,381
Total Fair Value	3,441,705	3,046,084
Total Unrealized Losses	57,277	61,537
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	34,243	64,023
Less than 12 Months, Unrealized Losses	443	644
12 Months or Longer, Fair Value	29,562	0
12 Months or Longer, Unrealized Losses	491	0
Total Fair Value	63,805	64,023
Total Unrealized Losses	934	644
Mortgage-backed securities issued by U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	36,810	128,121
Less than 12 Months, Unrealized Losses	357	1,240
12 Months or Longer, Fair Value	55,740	3,626
12 Months or Longer, Unrealized Losses	1,005	114
Total Fair Value	92,550	131,747
Total Unrealized Losses	1,362	1,354
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,271,012	2,123,181
Less than 12 Months, Unrealized Losses	10,263	42,571
12 Months or Longer, Fair Value	929,223	0
12 Months or Longer, Unrealized Losses	21,091	0
Total Fair Value	2,200,235	2,123,181
Total Unrealized Losses	31,354	42,571
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	653,781	682,492
Less than 12 Months, Unrealized Losses	9,497	15,653
12 Months or Longer, Fair Value	426,237	24,801
12 Months or Longer, Unrealized Losses	13,907	908
Total Fair Value	1,080,018	707,293
Total Unrealized Losses	23,404	16,561
Corporate debt and other securities
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	5,097	4,888
12 Months or Longer, Unrealized Losses	223	359
Total Fair Value	5,097	19,840
Total Unrealized Losses	$ 223	$ 407