Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Investment [Line Items]
Amortized Cost	$ 8,526,772	$ 8,715,456
Fair Value	8,412,376	8,725,442
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Amortized Cost	925,260	917,494
Fair Value	911,092	917,147
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	52,660
Fair Value	52,603
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	645,431
Fair Value	634,819
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	157,967
Fair Value	155,108
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	69,202
Fair Value	68,562
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Amortized Cost	316,982	408,266
Fair Value	311,361	406,363
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	117,562
Fair Value	117,444
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	121,584
Fair Value	119,743
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	34,984
Fair Value	33,946
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	42,852
Fair Value	40,228
State And Municipal Obligations [Member]
Investment [Line Items]
Amortized Cost	1,378,770	1,592,707
Fair Value	1,379,164	1,611,366
State And Municipal Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	147,325
Fair Value	147,668
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	598,663
Fair Value	600,688
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	591,819
Fair Value	590,950
State And Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	40,963
Fair Value	39,858
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	3,194,764	3,046,701
Fair Value	3,131,025	3,040,913
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	1,019,545	903,920
Fair Value	1,010,331	905,793
Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	1,351,461	1,495,380
Fair Value	1,338,542	1,492,800
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	5,565,770	5,446,001
Fair Value	5,479,898	5,439,506
Other Debt Securities [Member]
Investment [Line Items]
Amortized Cost	339,990	350,988
Fair Value	330,861	$ 351,060
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	9,003
Fair Value	8,971
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	257,704
Fair Value	252,151
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	73,283
Fair Value	$ 69,739