Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Less than 12 months, Fair Value	$ 431,911	$ 1,213,809
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,841	11,098
12 months or longer, Fair Value	1,491,101	4,221,687
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8,105	88,726
Total, Fair Value	1,923,012	5,435,496
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	9,946	99,824
U.S. Government and Federal Agency Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	3,568	317,699
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	23	6,515
12 months or longer, Fair Value	89,497	116,728
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	630	4,864
Total, Fair Value	93,065	434,427
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	653	11,379
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	14,899	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	0
12 months or longer, Fair Value	36,326	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	118	3,747
Total, Fair Value	51,225	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	121	3,747
State and Municipal Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	6,815	157,838
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	704
12 months or longer, Fair Value	23,389	257,051
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	45	4,326
Total, Fair Value	30,204	414,889
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	59	5,030
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	101,403	330,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	116	1,502
12 months or longer, Fair Value	603,083	1,927,268
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,533	46,766
Total, Fair Value	704,486	2,258,201
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	4,649	48,268
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	25,463	207,506
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	67	1,085
12 months or longer, Fair Value	440,616	657,685
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,850	11,694
Total, Fair Value	466,079	865,191
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,917	12,779
Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	274,765	147,997
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,617	728
12 months or longer, Fair Value	270,243	813,427
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	883	10,483
Total, Fair Value	545,008	961,424
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2,500	11,211
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	401,631	686,436
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,800	3,315
12 months or longer, Fair Value	1,313,942	3,398,380
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	7,266	68,943
Total, Fair Value	1,715,573	4,084,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	9,066	72,258
Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	4,998	51,836
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	564
12 months or longer, Fair Value	27,947	260,682
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	46	6,846
Total, Fair Value	32,945	312,518
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 47	$ 7,410