Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Investment [Line Items]
Less than 12 months, Fair Value	$ 5,061,104	$ 4,015,697
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	91,094	24,201
12 months or longer, Fair Value	2,391,086	1,156,715
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	82,076	19,921
Total, Fair Value	7,452,190	5,172,412
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	173,170	44,122
AFS securities in loss position at period-end, change in unrealized loss	129,000
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	572,747	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	12,285	4,443
12 months or longer, Fair Value	270,313	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9,072	0
Total, Fair Value	843,060	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	21,357	4,443
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	139,520	286,393
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,909	1,712
12 months or longer, Fair Value	81,596	49,766
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,055	217
Total, Fair Value	221,116	336,159
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	6,964	1,929
State And Municipal Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	715,673	282,843
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7,472	1,752
12 months or longer, Fair Value	130,190	49,339
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,817	1,002
Total, Fair Value	845,863	332,182
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	12,289	2,754
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	1,958,646	1,320,689
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	42,485	9,433
12 months or longer, Fair Value	1,039,348	619,300
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	46,000	14,311
Total, Fair Value	2,997,994	1,939,989
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	88,485	23,744
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	680,691	577,017
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,372	2,966
12 months or longer, Fair Value	374,601	153,813
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8,839	1,871
Total, Fair Value	1,055,292	730,830
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	18,211	4,837
Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	735,808	786,048
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,758	3,168
12 months or longer, Fair Value	422,531	264,295
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6,741	2,069
Total, Fair Value	1,158,339	1,050,343
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	16,499	5,237
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	3,375,145	2,683,754
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	61,615	15,567
12 months or longer, Fair Value	1,836,480	1,037,408
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	61,580	18,251
Total, Fair Value	5,211,625	3,721,162
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	123,195	33,818
Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	258,019	144,090
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,813	727
12 months or longer, Fair Value	72,507	20,202
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,552	451
Total, Fair Value	330,526	164,292
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 9,365	$ 1,178