Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 8,594,473	$ 8,602,599
Debt Securities, Available-for-sale, Fair Value	8,627,890	8,538,041
U.S. Government and Federal Agency Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	867,278	914,486
Debt Securities, Available-for-sale, Fair Value	877,921	907,652
U.S. Government and Federal Agency Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	29,484
Debt Securities, Available-for-sale, Fair Value	29,341
U.S. Government and Federal Agency Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	588,651
Debt Securities, Available-for-sale, Fair Value	597,792
U.S. Government and Federal Agency Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	249,143
Debt Securities, Available-for-sale, Fair Value	250,788
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	199,496	199,470
Debt Securities, Available-for-sale, Fair Value	197,979	195,778
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	36,442
Debt Securities, Available-for-sale, Fair Value	36,176
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	85,155
Debt Securities, Available-for-sale, Fair Value	84,759
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	34,986
Debt Securities, Available-for-sale, Fair Value	34,974
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,913
Debt Securities, Available-for-sale, Fair Value	42,070
State and Municipal Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,248,401	1,322,785
Debt Securities, Available-for-sale, Fair Value	1,274,200	1,328,039
State and Municipal Obligations [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	87,817
Debt Securities, Available-for-sale, Fair Value	88,067
State and Municipal Obligations [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	663,990
Debt Securities, Available-for-sale, Fair Value	675,122
State and Municipal Obligations [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	440,363
Debt Securities, Available-for-sale, Fair Value	454,085
State and Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	56,231
Debt Securities, Available-for-sale, Fair Value	56,926
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,416,497	3,253,433
Debt Securities, Available-for-sale, Fair Value	3,412,399	3,214,985
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,056,738	1,053,854
Debt Securities, Available-for-sale, Fair Value	1,060,008	1,047,716
Asset-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,470,541	1,518,976
Debt Securities, Available-for-sale, Fair Value	1,470,516	1,511,614
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,943,776	5,826,263
Debt Securities, Available-for-sale, Fair Value	5,942,923	5,774,315
Other Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	335,522	339,595
Debt Securities, Available-for-sale, Fair Value	334,867	$ 332,257
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	22,497
Debt Securities, Available-for-sale, Fair Value	22,412
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	245,030
Debt Securities, Available-for-sale, Fair Value	244,892
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	67,995
Debt Securities, Available-for-sale, Fair Value	$ 67,563