Investment Securities (Securities With Unrealized Losses And Length Of Impairment Period) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Less than 12 months, Fair Value	$ 2,236,597	$ 4,036,153
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	18,880	50,837
12 months or longer, Fair Value	756,589	444,252
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9,472	10,105
Total, Fair Value	2,993,186	4,480,405
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	28,352	60,942
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	123,071	349,538
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,979	2,823
12 months or longer, Fair Value	0	32,208
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	3,489
Total, Fair Value	123,071	381,746
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3,979	6,312
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	190,141	190,441
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,650	1,576
12 months or longer, Fair Value	49,793	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	183	0
Total, Fair Value	239,934	190,441
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,833	1,576
State And Municipal Obligations [Member]
Investment [Line Items]
Less than 12 months, Fair Value	95,890	700,779
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	692	12,164
12 months or longer, Fair Value	38,026	15,195
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	993	529
Total, Fair Value	133,916	715,974
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,685	12,693
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	887,047	1,147,416
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,741	20,638
12 months or longer, Fair Value	223,550	2,150
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,442	5
Total, Fair Value	1,110,597	1,149,566
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	13,183	20,643
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	381,896	688,131
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,674	6,373
12 months or longer, Fair Value	156,455	34,946
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,177	120
Total, Fair Value	538,351	723,077
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3,851	6,493
Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	488,409	780,209
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	522	5,277
12 months or longer, Fair Value	279,402	358,778
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,563	5,936
Total, Fair Value	767,811	1,138,987
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3,085	11,213
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	1,757,352	2,615,756
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11,937	32,288
12 months or longer, Fair Value	659,407	395,874
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8,182	6,061
Total, Fair Value	2,416,759	3,011,630
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	20,119	38,349
Debt Securities [Member]
Investment [Line Items]
Less than 12 months, Fair Value	70,143	179,639
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	622	1,986
12 months or longer, Fair Value	9,363	975
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	114	26
Total, Fair Value	79,506	180,614
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 736	$ 2,012