Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 12,538,550,000	$ 13,738,206,000
Fair Value	11,228,616,000	12,238,316,000
U.S. government and federal agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,048,755,000	1,078,807,000
Fair Value	1,020,223,000	1,035,406,000
U.S. government and federal agency obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	482,979,000
Fair Value	474,435,000
U.S. government and federal agency obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	391,902,000
Fair Value	378,408,000
U.S. government and federal agency obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	173,874,000
Fair Value	167,380,000
Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,689,000	55,729,000
Fair Value	44,414,000	43,108,000
Government-sponsored enterprise obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,955,000
Fair Value	4,631,000
Government-sponsored enterprise obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50,734,000
Fair Value	39,783,000
State and municipal obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,615,170,000	1,965,028,000
Fair Value	1,453,814,000	1,767,109,000
State and municipal obligations [Member] | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	98,381,000
Fair Value	97,510,000
State and municipal obligations [Member] | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	465,196,000
Fair Value	442,933,000
State and municipal obligations [Member] | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	887,757,000
Fair Value	771,946,000
State and municipal obligations [Member] | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	163,836,000
Fair Value	141,425,000
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,975,242,000	5,087,893,000
Fair Value	4,271,563,000	4,308,427,000
Non-Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,403,543,000	1,423,469,000
Fair Value	1,207,969,000	1,211,607,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,918,160,000	3,588,025,000
Fair Value	2,763,578,000	3,397,801,000
Total Mortgage And Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,296,945,000	10,099,387,000
Fair Value	8,243,110,000	8,917,835,000
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	521,991,000	539,255,000
Fair Value	467,055,000	$ 474,858,000
Other debt securities | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	14,040,000
Fair Value	13,572,000
Other debt securities | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	246,688,000
Fair Value	230,527,000
Other debt securities | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	245,003,000
Fair Value	209,285,000
Other debt securities | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	16,260,000
Fair Value	$ 13,671,000