Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Less than 12 months, Fair Value	$ 857,830	$ 1,213,809
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,488	11,098
12 months or longer, Fair Value	733,953	4,221,687
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,053	88,726
Total, Fair Value	1,591,783	5,435,496
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	6,541	99,824
U.S. Government and Federal Agency Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	90,662	317,699
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	126	6,515
12 months or longer, Fair Value	52,930	116,728
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	426	4,864
Total, Fair Value	143,592	434,427
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	552	11,379
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
12 months or longer, Fair Value	36,409	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	38	3,747
Total, Fair Value	36,409	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	38	3,747
State and Municipal Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	15,726	157,838
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	704
12 months or longer, Fair Value	1,551	257,051
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4	4,326
Total, Fair Value	17,277	414,889
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	13	5,030
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	343,820	330,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,271	1,502
12 months or longer, Fair Value	182,805	1,927,268
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	865	46,766
Total, Fair Value	526,625	2,258,201
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2,136	48,268
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	38,085	207,506
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	103	1,085
12 months or longer, Fair Value	311,040	657,685
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	928	11,694
Total, Fair Value	349,125	865,191
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,031	12,779
Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	369,537	147,997
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,979	728
12 months or longer, Fair Value	140,726	813,427
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	784	10,483
Total, Fair Value	510,263	961,424
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2,763	11,211
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	751,442	686,436
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,353	3,315
12 months or longer, Fair Value	634,571	3,398,380
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,577	68,943
Total, Fair Value	1,386,013	4,084,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	5,930	72,258
Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	0	51,836
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	564
12 months or longer, Fair Value	8,492	260,682
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8	6,846
Total, Fair Value	8,492	312,518
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 8	$ 7,410