Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Amortized Cost	$ 9,341,771	$ 9,600,330
Fair Value	9,439,701	9,649,203
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Amortized Cost	912,028	919,904
Fair Value	912,555	920,904
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	58,665
Fair Value	58,829
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	499,601
Fair Value	502,990
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	318,318
Fair Value	318,212
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	35,444
Fair Value	32,524
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Amortized Cost	446,864	450,448
Fair Value	446,285	449,998
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	98,069
Fair Value	98,206
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	336,302
Fair Value	335,723
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	12,493
Fair Value	12,356
State And Municipal Obligations [Member]
Investment [Line Items]
Amortized Cost	1,745,068	1,778,684
Fair Value	1,777,797	1,778,214
State And Municipal Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	171,936
Fair Value	172,890
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	643,200
Fair Value	654,145
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	879,036
Fair Value	900,292
State And Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	50,896
Fair Value	50,470
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	2,604,217	2,674,964
Fair Value	2,620,198	2,685,931
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	1,063,236	1,054,446
Fair Value	1,066,889	1,055,639
Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	2,249,399	2,389,176
Fair Value	2,250,426	2,381,301
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	5,916,852	6,118,586
Fair Value	5,937,513	6,122,871
Other Debt Securities [Member]
Investment [Line Items]
Amortized Cost	315,496	327,030
Fair Value	317,704	325,953
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	13,387
Fair Value	13,389
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	176,199
Fair Value	177,812
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	125,910
Fair Value	126,503
Equity Securities [Member]
Investment [Line Items]
Amortized Cost	5,463	5,678
Fair Value	$ 47,847	$ 51,263