Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 8,496,993	$ 8,602,599
Debt Securities, Available-for-sale, Fair Value	8,660,419	8,538,041
U.S. Government and Federal Agency Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	826,551	914,486
Debt Securities, Available-for-sale, Fair Value	849,877	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	57,175
Debt Securities, Available-for-sale, Fair Value	56,726
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	516,924
Debt Securities, Available-for-sale, Fair Value	533,605
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	252,452
Debt Securities, Available-for-sale, Fair Value	259,546
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	167,683	199,470
Debt Securities, Available-for-sale, Fair Value	168,817	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	51,562
Debt Securities, Available-for-sale, Fair Value	51,551
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	55,049
Debt Securities, Available-for-sale, Fair Value	55,162
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	34,987
Debt Securities, Available-for-sale, Fair Value	35,032
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	26,085
Debt Securities, Available-for-sale, Fair Value	27,072
State and Municipal Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,163,411	1,322,785
Debt Securities, Available-for-sale, Fair Value	1,203,495	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	57,870
Debt Securities, Available-for-sale, Fair Value	58,039
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	709,484
Debt Securities, Available-for-sale, Fair Value	728,639
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	354,519
Debt Securities, Available-for-sale, Fair Value	374,236
State and Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	41,538
Debt Securities, Available-for-sale, Fair Value	42,581
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,791,709	3,253,433
Debt Securities, Available-for-sale, Fair Value	3,858,575	3,214,985
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	921,080	1,053,854
Debt Securities, Available-for-sale, Fair Value	936,577	1,047,716
Asset-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,288,360	1,518,976
Debt Securities, Available-for-sale, Fair Value	1,298,835	1,511,614
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	6,001,149	5,826,263
Debt Securities, Available-for-sale, Fair Value	6,093,987	5,774,315
Other Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	338,199	339,595
Debt Securities, Available-for-sale, Fair Value	344,243	$ 332,257
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	43,894
Debt Securities, Available-for-sale, Fair Value	43,965
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	239,692
Debt Securities, Available-for-sale, Fair Value	243,606
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	54,613
Debt Securities, Available-for-sale, Fair Value	$ 56,672