Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Investment [Line Items]
Less than 12 months, Fair Value	$ 5,405,253	$ 4,015,697
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	102,133	24,201
12 months or longer, Fair Value	1,086,893	1,156,715
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	35,441	19,921
Total, Fair Value	6,492,146	5,172,412
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	137,574	44,122
AFS securities in loss position at period-end, change in unrealized loss	93,500
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	707,018	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	12,156	4,443
12 months or longer, Fair Value	90,340	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,515	0
Total, Fair Value	797,358	618,617
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	14,671	4,443
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	261,378	286,393
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,605	1,712
12 months or longer, Fair Value	49,983	49,766
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	16	217
Total, Fair Value	311,361	336,159
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	5,621	1,929
State And Municipal Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	458,880	282,843
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,700	1,752
12 months or longer, Fair Value	51,863	49,339
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,011	1,002
Total, Fair Value	510,743	332,182
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	7,711	2,754
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	2,029,957	1,320,689
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	45,267	9,433
12 months or longer, Fair Value	566,986	619,300
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	24,467	14,311
Total, Fair Value	2,596,943	1,939,989
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	69,734	23,744
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	773,890	577,017
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	12,076	2,966
12 months or longer, Fair Value	134,679	153,813
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,370	1,871
Total, Fair Value	908,569	730,830
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	15,446	4,837
Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	862,416	786,048
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	13,296	3,168
12 months or longer, Fair Value	173,895	264,295
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,966	2,069
Total, Fair Value	1,036,311	1,050,343
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	15,262	5,237
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	3,666,263	2,683,754
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	70,639	15,567
12 months or longer, Fair Value	875,560	1,037,408
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	29,803	18,251
Total, Fair Value	4,541,823	3,721,162
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	100,442	33,818
Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	311,714	144,090
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8,033	727
12 months or longer, Fair Value	19,147	20,202
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,096	451
Total, Fair Value	330,861	164,292
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 9,129	$ 1,178