Investment Securities (Available For Sale Securities Unrealized Gains And Losses, By Security Type) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Investment [Line Items]
Amortized Cost	$ 9,212,096	$ 9,691,414
Gross unreailzed gain in accumulated other comprehensive income at period end	237,729	138,210
Gross unreailzed losses in accumulated other comprehensive income at period end	(10,954)	(52,620)
Fair Value	9,438,871	9,777,004
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Amortized Cost	738,658	729,846
Gross unreailzed gain in accumulated other comprehensive income at period end	19,132	5,051
Gross unreailzed losses in accumulated other comprehensive income at period end	(2,141)	(7,821)
Fair Value	755,649	727,076
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Amortized Cost	445,648	794,912
Gross unreailzed gain in accumulated other comprehensive income at period end	5,637	2,657
Gross unreailzed losses in accumulated other comprehensive income at period end	(43)	(4,546)
Fair Value	451,242	793,023
State And Municipal Obligations [Member]
Investment [Line Items]
Amortized Cost	1,776,857	1,706,635
Gross unreailzed gain in accumulated other comprehensive income at period end	59,760	37,061
Gross unreailzed losses in accumulated other comprehensive income at period end	(616)	(1,739)
Fair Value	1,836,001	1,741,957
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	2,590,902	2,579,031
Gross unreailzed gain in accumulated other comprehensive income at period end	72,803	47,856
Gross unreailzed losses in accumulated other comprehensive income at period end	(28)	(8,606)
Fair Value	2,663,677	2,618,281
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	922,302	879,186
Gross unreailzed gain in accumulated other comprehensive income at period end	15,145	8,596
Gross unreailzed losses in accumulated other comprehensive income at period end	(239)	(7,819)
Fair Value	937,208	879,963
Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	2,403,019	2,660,201
Gross unreailzed gain in accumulated other comprehensive income at period end	14,026	1,287
Gross unreailzed losses in accumulated other comprehensive income at period end	(7,721)	(17,107)
Fair Value	2,409,324	2,644,381
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	5,916,223	6,118,418
Gross unreailzed gain in accumulated other comprehensive income at period end	101,974	57,739
Gross unreailzed losses in accumulated other comprehensive income at period end	(7,988)	(33,532)
Fair Value	6,010,209	6,142,625
Other Debt Securities [Member]
Investment [Line Items]
Amortized Cost	329,032	335,925
Gross unreailzed gain in accumulated other comprehensive income at period end	9,946	377
Gross unreailzed losses in accumulated other comprehensive income at period end	(166)	(4,982)
Fair Value	338,812	331,320
Equity Securities [Member]
Investment [Line Items]
Amortized Cost	5,678	5,678
Gross unreailzed gain in accumulated other comprehensive income at period end	41,280	35,325
Gross unreailzed losses in accumulated other comprehensive income at period end	0	0
Fair Value	$ 46,958	$ 41,003