Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 8,546,590	$ 8,602,599
Debt Securities, Available-for-sale, Fair Value	8,682,303	8,538,041
U.S. Government and Federal Agency Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	824,830	914,486
Debt Securities, Available-for-sale, Fair Value	845,939	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	57,062
Debt Securities, Available-for-sale, Fair Value	56,474
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	515,684
Debt Securities, Available-for-sale, Fair Value	531,338
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	252,084
Debt Securities, Available-for-sale, Fair Value	258,127
Government-Sponsored Enterprise Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	199,521	199,470
Debt Securities, Available-for-sale, Fair Value	200,137	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	36,444
Debt Securities, Available-for-sale, Fair Value	36,326
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	85,157
Debt Securities, Available-for-sale, Fair Value	85,247
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	35,061
Government-Sponsored Enterprise Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	42,934
Debt Securities, Available-for-sale, Fair Value	43,503
State and Municipal Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,199,829	1,322,785
Debt Securities, Available-for-sale, Fair Value	1,237,456	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	80,688
Debt Securities, Available-for-sale, Fair Value	80,910
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	651,274
Debt Securities, Available-for-sale, Fair Value	667,864
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	416,248
Debt Securities, Available-for-sale, Fair Value	435,736
State and Municipal Obligations [Member] | Available For Sale Maturity After10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	51,619
Debt Securities, Available-for-sale, Fair Value	52,946
Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,680,963	3,253,433
Debt Securities, Available-for-sale, Fair Value	3,729,632	3,214,985
Non-Agency Mortgage-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	996,413	1,053,854
Debt Securities, Available-for-sale, Fair Value	1,010,667	1,047,716
Asset-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	1,316,766	1,518,976
Debt Securities, Available-for-sale, Fair Value	1,326,178	1,511,614
Total Mortgage And Asset-Backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,994,142	5,826,263
Debt Securities, Available-for-sale, Fair Value	6,066,477	5,774,315
Other Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	328,268	339,595
Debt Securities, Available-for-sale, Fair Value	332,294	$ 332,257
Other Debt Securities [Member] | Available For Sale Securities Maturity Within1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	27,495
Debt Securities, Available-for-sale, Fair Value	27,458
Other Debt Securities [Member] | Available For Sale Securities Maturity After1 But Within5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	246,153
Debt Securities, Available-for-sale, Fair Value	249,059
Other Debt Securities [Member] | Available For Sale Securities Maturity After5 But Within10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	54,620
Debt Securities, Available-for-sale, Fair Value	$ 55,777