Investment Securities (Schedule Of Unrealized Loss On Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 2,398,812	$ 1,995,846
Less than 12 Months, Unrealized Losses	57,879	20,560
12 Months or Longer, Fair Value	1,402,159	1,445,859
12 Months or Longer, Unrealized Losses	55,703	36,717
Total Fair Value, Fair Value	3,800,971	3,441,705
Total Fair Value, Unrealized Losses	113,582	57,277
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	72,694	34,243
Less than 12 Months, Unrealized Losses	989	443
12 Months or Longer, Fair Value	29,313	29,562
12 Months or Longer, Unrealized Losses	735	491
Total Fair Value, Fair Value	102,007	63,805
Total Fair Value, Unrealized Losses	1,724	934
Mortgage-backed securities issued by U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	39,763	36,810
Less than 12 Months, Unrealized Losses	1,045	357
12 Months or Longer, Fair Value	52,763	55,740
12 Months or Longer, Unrealized Losses	2,212	1,005
Total Fair Value, Fair Value	92,526	92,550
Total Fair Value, Unrealized Losses	3,257	1,362
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,656,562	1,271,012
Less than 12 Months, Unrealized Losses	38,195	10,263
12 Months or Longer, Fair Value	882,984	929,223
12 Months or Longer, Unrealized Losses	32,938	21,091
Total Fair Value, Fair Value	2,539,546	2,200,235
Total Fair Value, Unrealized Losses	71,133	31,354
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	629,793	653,781
Less than 12 Months, Unrealized Losses	17,650	9,497
12 Months or Longer, Fair Value	435,247	426,237
12 Months or Longer, Unrealized Losses	19,670	13,907
Total Fair Value, Fair Value	1,065,040	1,080,018
Total Fair Value, Unrealized Losses	37,320	23,404
Corporate debt and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Longer, Fair Value	1,852	5,097
12 Months or Longer, Unrealized Losses	148	223
Total Fair Value, Fair Value	1,852	5,097
Total Fair Value, Unrealized Losses	$ 148	$ 223