Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Less than 12 months, Fair Value	$ 1,213,809	$ 4,015,697
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11,098	24,201
12 months or longer, Fair Value	4,221,687	1,156,715
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	88,726	19,921
Total, Fair Value	5,435,496	5,172,412
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	99,824	44,122
US Treasury and Government [Member]
Investment [Line Items]
Less than 12 months, Fair Value	317,699	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6,515	4,443
12 months or longer, Fair Value	116,728	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,864	0
Total, Fair Value	434,427	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	11,379	4,443
US Government-sponsored Enterprise Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	0	286,393
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	1,712
12 months or longer, Fair Value	188,846	49,766
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,747	217
Total, Fair Value	188,846	336,159
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3,747	1,929
State and municipal obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	157,838	282,843
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	704	1,752
12 months or longer, Fair Value	257,051	49,339
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,326	1,002
Total, Fair Value	414,889	332,182
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	5,030	2,754
Agency mortgage-backed securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	330,933	1,320,689
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,502	9,433
12 months or longer, Fair Value	1,927,268	619,300
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	46,766	14,311
Total, Fair Value	2,258,201	1,939,989
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	48,268	23,744
Non-agency mortgage-backed securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	207,506	577,017
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,085	2,966
12 months or longer, Fair Value	657,685	153,813
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11,694	1,871
Total, Fair Value	865,191	730,830
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	12,779	4,837
Asset-backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	147,997	786,048
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	728	3,168
12 months or longer, Fair Value	813,427	264,295
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10,483	2,069
Total, Fair Value	961,424	1,050,343
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	11,211	5,237
Total mortgage and asset-backed securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	686,436	2,683,754
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,315	15,567
12 months or longer, Fair Value	3,398,380	1,037,408
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	68,943	18,251
Total, Fair Value	4,084,816	3,721,162
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	72,258	33,818
Other debt securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	51,836	144,090
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	564	727
12 months or longer, Fair Value	260,682	20,202
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6,846	451
Total, Fair Value	312,518	164,292
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 7,410	$ 1,178