Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Amortized Cost	$ 8,971,612	$ 9,600,330
Fair Value	9,109,287	9,649,203
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Amortized Cost	916,224	919,904
Fair Value	918,604	920,904
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	57,511
Fair Value	58,238
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	570,284
Fair Value	573,789
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	218,912
Fair Value	219,468
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	69,517
Fair Value	67,109
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Amortized Cost	470,403	450,448
Fair Value	469,414	449,998
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	187,032
Fair Value	187,027
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	247,444
Fair Value	247,141
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	35,927
Fair Value	35,246
State And Municipal Obligations [Member]
Investment [Line Items]
Amortized Cost	1,687,136	1,778,684
Fair Value	1,720,403	1,778,214
State And Municipal Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	177,616
Fair Value	178,836
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	659,012
Fair Value	671,931
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	800,504
Fair Value	819,943
State And Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	50,004
Fair Value	49,693
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	2,741,329	2,674,964
Fair Value	2,756,973	2,685,931
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	1,062,079	1,054,446
Fair Value	1,066,764	1,055,639
Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	1,735,004	2,389,176
Fair Value	1,736,966	2,381,301
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	5,538,412	6,118,586
Fair Value	5,560,703	6,122,871
Other Debt Securities [Member]
Investment [Line Items]
Amortized Cost	354,084	327,030
Fair Value	356,641	325,953
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	13,388
Fair Value	13,393
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	207,556
Fair Value	210,022
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	133,140
Fair Value	133,226
Equity Securities [Member]
Investment [Line Items]
Amortized Cost	5,353	5,678
Fair Value	$ 83,522	$ 51,263