Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 11,833,736,000	$ 13,738,206,000
Fair Value	10,414,625,000	12,238,316,000
U.S. government and federal agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	984,984,000	1,078,807,000
Fair Value	945,815,000	1,035,406,000
U.S. government and federal agency obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	464,203,000
Fair Value	455,044,000
U.S. government and federal agency obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	344,689,000
Fair Value	327,450,000
U.S. government and federal agency obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	176,092,000
Fair Value	163,321,000
Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,681,000	55,729,000
Fair Value	44,036,000	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	4,418,000
Government-sponsored enterprise obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50,726,000
Fair Value	39,618,000
State and municipal obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,401,610,000	1,965,028,000
Fair Value	1,227,737,000	1,767,109,000
State and municipal obligations [Member] | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	77,600,000
Fair Value	76,353,000
State and municipal obligations [Member] | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	346,058,000
Fair Value	318,691,000
State and municipal obligations [Member] | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	826,895,000
Fair Value	704,751,000
State and municipal obligations [Member] | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	151,057,000
Fair Value	127,942,000
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,849,215,000	5,087,893,000
Fair Value	4,065,406,000	4,308,427,000
Non-Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,378,516,000	1,423,469,000
Fair Value	1,174,790,000	1,211,607,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,646,850,000	3,588,025,000
Fair Value	2,499,675,000	3,397,801,000
Total Mortgage And Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,874,581,000	10,099,387,000
Fair Value	7,739,871,000	8,917,835,000
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	516,880,000	539,255,000
Fair Value	457,166,000	$ 474,858,000
Other debt securities | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	35,141,000
Fair Value	34,128,000
Other debt securities | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	221,479,000
Fair Value	204,297,000
Other debt securities | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	244,000,000
Fair Value	205,179,000
Other debt securities | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	16,260,000
Fair Value	$ 13,562,000