Investment Securities (Schedule Of Unrealized Loss On Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 2,989,625	$ 3,012,769
Less than 12 Months, Unrealized Losses	44,161	60,156
12 Months or Longer, Fair Value	28,281	33,315
12 Months or Longer, Unrealized Losses	1,000	1,381
Total Fair Value, Fair Value	3,017,906	3,046,084
Total Fair Value, Unrealized Losses	45,161	61,537
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	64,342	64,023
Less than 12 Months, Unrealized Losses	360	644
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value, Fair Value	64,342	64,023
Total Fair Value, Unrealized Losses	360	644
Mortgage-backed securities issued by U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	95,492	128,121
Less than 12 Months, Unrealized Losses	1,125	1,240
12 Months or Longer, Fair Value	0	3,626
12 Months or Longer, Unrealized Losses	0	114
Total Fair Value, Fair Value	95,492	131,747
Total Fair Value, Unrealized Losses	1,125	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	2,161,449	2,123,181
Less than 12 Months, Unrealized Losses	30,998	42,571
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value, Fair Value	2,161,449	2,123,181
Total Fair Value, Unrealized Losses	30,998	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	668,342	682,492
Less than 12 Months, Unrealized Losses	11,678	15,653
12 Months or Longer, Fair Value	23,212	24,801
12 Months or Longer, Unrealized Losses	790	908
Total Fair Value, Fair Value	691,554	707,293
Total Fair Value, Unrealized Losses	12,468	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	5,069	4,888
12 Months or Longer, Unrealized Losses	210	359
Total Fair Value, Fair Value	5,069	19,840
Total Fair Value, Unrealized Losses	$ 210	$ 407