Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Less than 12 months, Fair Value	$ 5,365,082	$ 4,015,697
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	83,127	24,201
12 months or longer, Fair Value	1,109,738	1,156,715
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	31,246	19,921
Total, Fair Value	6,474,820	5,172,412
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	114,373	44,122
AFS securities in loss position at period-end, change in unrealized loss	70,300
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	653,945	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,647	4,443
12 months or longer, Fair Value	59,435	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,872	0
Total, Fair Value	713,380	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	11,519	4,443
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	338,752	286,393
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,588	1,712
12 months or longer, Fair Value	49,847	49,766
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	144	217
Total, Fair Value	388,599	336,159
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	4,732	1,929
State And Municipal Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	529,699	282,843
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6,427	1,752
12 months or longer, Fair Value	44,474	49,339
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,749	1,002
Total, Fair Value	574,173	332,182
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8,176	2,754
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	1,922,859	1,320,689
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	35,455	9,433
12 months or longer, Fair Value	591,341	619,300
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	21,600	14,311
Total, Fair Value	2,514,200	1,939,989
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	57,055	23,744
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	729,615	577,017
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,447	2,966
12 months or longer, Fair Value	137,775	153,813
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,872	1,871
Total, Fair Value	867,390	730,830
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	12,319	4,837
Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	884,800	786,048
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11,101	3,168
12 months or longer, Fair Value	207,087	264,295
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,134	2,069
Total, Fair Value	1,091,887	1,050,343
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	13,235	5,237
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	3,537,274	2,683,754
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	56,003	15,567
12 months or longer, Fair Value	936,203	1,037,408
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	26,606	18,251
Total, Fair Value	4,473,477	3,721,162
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	82,609	33,818
Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	305,412	144,090
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6,462	727
12 months or longer, Fair Value	19,779	20,202
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	875	451
Total, Fair Value	325,191	164,292
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 7,337	$ 1,178