Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Less than 12 months, Fair Value	$ 511,028	$ 1,213,809
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,371	11,098
12 months or longer, Fair Value	3,607,517	4,221,687
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	39,790	88,726
Total, Fair Value	4,118,545	5,435,496
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	41,161	99,824
U.S. Government and Federal Agency Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	3,200	317,699
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	26	6,515
12 months or longer, Fair Value	114,835	116,728
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,175	4,864
Total, Fair Value	118,035	434,427
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,201	11,379
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	34,974	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	12	0
12 months or longer, Fair Value	139,959	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,763	3,747
Total, Fair Value	174,933	188,846
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,775	3,747
State and Municipal Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	13,907	157,838
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	704
12 months or longer, Fair Value	110,737	257,051
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	683	4,326
Total, Fair Value	124,644	414,889
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	686	5,030
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	156,031	330,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	326	1,502
12 months or longer, Fair Value	1,706,133	1,927,268
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	23,749	46,766
Total, Fair Value	1,862,164	2,258,201
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	24,075	48,268
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	47,338	207,506
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	41	1,085
12 months or longer, Fair Value	639,311	657,685
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6,522	11,694
Total, Fair Value	686,649	865,191
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	6,563	12,779
Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	219,611	147,997
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	931	728
12 months or longer, Fair Value	726,118	813,427
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,630	10,483
Total, Fair Value	945,729	961,424
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	5,561	11,211
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	422,980	686,436
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,298	3,315
12 months or longer, Fair Value	3,071,562	3,398,380
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	34,901	68,943
Total, Fair Value	3,494,542	4,084,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	36,199	72,258
Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	35,967	51,836
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	32	564
12 months or longer, Fair Value	170,424	260,682
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,268	6,846
Total, Fair Value	206,391	312,518
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 1,300	$ 7,410