Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 8,832,289	$ 8,715,456
Available-for-sale Securities, Debt Securities	8,674,986	8,725,442
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	922,431	917,494
Available-for-sale Securities, Debt Securities	901,115	917,147
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	23,624
Available-for-sale Securities, Debt Securities	23,532
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	646,024
Available-for-sale Securities, Debt Securities	632,363
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	183,500
Available-for-sale Securities, Debt Securities	177,790
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	69,283
Available-for-sale Securities, Debt Securities	67,430
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	228,080	408,266
Available-for-sale Securities, Debt Securities	221,116	406,363
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	28,635
Available-for-sale Securities, Debt Securities	28,607
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	121,588
Available-for-sale Securities, Debt Securities	119,494
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	34,985
Available-for-sale Securities, Debt Securities	33,587
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	42,872
Available-for-sale Securities, Debt Securities	39,428
State And Municipal Obligations [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,397,646	1,592,707
Available-for-sale Securities, Debt Securities	1,388,898	1,611,366
State And Municipal Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	124,946
Available-for-sale Securities, Debt Securities	125,248
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	642,000
Available-for-sale Securities, Debt Securities	640,269
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	551,184
Available-for-sale Securities, Debt Securities	545,707
State And Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	79,516
Available-for-sale Securities, Debt Securities	77,674
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	3,351,134	3,046,701
Available-for-sale Securities, Debt Securities	3,266,524	3,040,913
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,103,357	903,920
Available-for-sale Securities, Debt Securities	1,091,382	905,793
Asset-Backed Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,489,750	1,495,380
Available-for-sale Securities, Debt Securities	1,475,425	1,492,800
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	5,944,241	5,446,001
Available-for-sale Securities, Debt Securities	5,833,331	5,439,506
Other Debt Securities [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	339,891	350,988
Available-for-sale Securities, Debt Securities	330,526	$ 351,060
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	9,002
Available-for-sale Securities, Debt Securities	8,984
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	257,635
Available-for-sale Securities, Debt Securities	251,880
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	73,254
Available-for-sale Securities, Debt Securities	$ 69,662