Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Amortized Cost	$ 8,520,428	$ 8,715,456
Fair Value	8,432,180	8,725,442
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Amortized Cost	921,825	917,494
Fair Value	911,923	917,147
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	52,205
Fair Value	52,521
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	644,016
Fair Value	636,542
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	156,769
Fair Value	154,484
U.S. Government And Federal Agency Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	68,835
Fair Value	68,376
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Amortized Cost	393,331	408,266
Fair Value	388,599	406,363
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	193,937
Fair Value	193,623
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	121,580
Fair Value	120,181
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	34,983
Fair Value	34,152
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	42,831
Fair Value	40,643
State And Municipal Obligations [Member]
Investment [Line Items]
Amortized Cost	1,417,449	1,592,707
Fair Value	1,416,845	1,611,366
State And Municipal Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	157,082
Fair Value	157,746
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	567,474
Fair Value	569,318
State And Municipal Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	649,164
Fair Value	646,866
State And Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Amortized Cost	43,729
Fair Value	42,915
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	3,003,975	3,046,701
Fair Value	2,954,994	3,040,913
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	966,401	903,920
Fair Value	960,612	905,793
Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	1,476,947	1,495,380
Fair Value	1,466,035	1,492,800
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Amortized Cost	5,447,323	5,446,001
Fair Value	5,381,641	5,439,506
Other Debt Securities [Member]
Investment [Line Items]
Amortized Cost	340,500	350,988
Fair Value	333,172	$ 351,060
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Amortized Cost	3,999
Fair Value	3,981
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Amortized Cost	262,778
Fair Value	258,315
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Amortized Cost	73,723
Fair Value	$ 70,876