Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Amortized Cost	$ 9,592,299	$ 9,600,330
Fair Value	9,671,975	9,649,203
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Amortized Cost	910,106	919,904
Fair Value	914,421	920,904
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	58,300
Fair Value	59,291
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	498,843
Fair Value	504,344
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	317,572
Fair Value	318,018
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	35,391
Fair Value	32,768
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Amortized Cost	450,559	450,448
Fair Value	450,206	449,998
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	28,975
Fair Value	29,025
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	412,289
Fair Value	411,880
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	9,295
Fair Value	9,301
State And Municipal Obligations [Member]
Investment [Line Items]
Amortized Cost	1,780,171	1,778,684
Fair Value	1,796,037	1,778,214
State And Municipal Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	208,310
Fair Value	209,638
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	607,968
Fair Value	616,965
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	911,634
Fair Value	918,378
State And Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	52,259
Fair Value	51,056
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	2,695,352	2,674,964
Fair Value	2,708,746	2,685,931
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	1,077,623	1,054,446
Fair Value	1,078,256	1,055,639
Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	2,345,961	2,389,176
Fair Value	2,343,637	2,381,301
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	6,118,936	6,118,586
Fair Value	6,130,639	6,122,871
Other Debt Securities [Member]
Investment [Line Items]
Amortized Cost	326,967	327,030
Fair Value	326,807	325,953
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	19,385
Fair Value	19,383
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	128,409
Fair Value	128,768
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	167,585
Fair Value	167,607
Other Debt Securities [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	11,588
Fair Value	11,049
Equity Securities [Member]
Investment [Line Items]
Amortized Cost	5,560	5,678
Fair Value	$ 53,865	$ 51,263