Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Less than 12 months, Fair Value	$ 1,136,297	$ 1,213,809
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,413	11,098
12 months or longer, Fair Value	517,817	4,221,687
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,451	88,726
Total, Fair Value	1,654,114	5,435,496
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	12,864	99,824
US Treasury and Government [Member]
Investment [Line Items]
Less than 12 months, Fair Value	31,787	317,699
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	21	6,515
12 months or longer, Fair Value	25,405	116,728
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	21	4,864
Total, Fair Value	57,192	434,427
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	42	11,379
US Government-sponsored Enterprise Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	6,155	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	187	0
12 months or longer, Fair Value	0	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	3,747
Total, Fair Value	6,155	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	187	3,747
State and municipal obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	6,700	157,838
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	31	704
12 months or longer, Fair Value	1,554	257,051
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	4,326
Total, Fair Value	8,254	414,889
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	32	5,030
Agency mortgage-backed securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	652,352	330,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,306	1,502
12 months or longer, Fair Value	147,653	1,927,268
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	867	46,766
Total, Fair Value	800,005	2,258,201
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	6,173	48,268
Non-agency mortgage-backed securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	102,931	207,506
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	254	1,085
12 months or longer, Fair Value	189,747	657,685
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	451	11,694
Total, Fair Value	292,678	865,191
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	705	12,779
Asset-backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	330,876	147,997
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,610	728
12 months or longer, Fair Value	152,461	813,427
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,108	10,483
Total, Fair Value	483,337	961,424
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	5,718	11,211
Total mortgage and asset-backed securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	1,086,159	686,436
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,170	3,315
12 months or longer, Fair Value	489,861	3,398,380
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,426	68,943
Total, Fair Value	1,576,020	4,084,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	12,596	72,258
Other debt securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	5,496	51,836
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	564
12 months or longer, Fair Value	997	260,682
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	6,846
Total, Fair Value	6,493	312,518
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 7	$ 7,410