Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)	Sep. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,176,324,000	$ 14,419,133,000
Fair Value	12,632,510,000	14,450,027,000
U.S. government and federal agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,084,984,000	1,035,477,000
Fair Value	1,036,325,000	1,080,720,000
U.S. government and federal agency obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	159,019,000
Fair Value	158,319,000
U.S. government and federal agency obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	735,831,000
Fair Value	705,287,000
U.S. government and federal agency obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	190,134,000
Fair Value	172,719,000
Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,737,000	50,773,000
Fair Value	43,175,000	51,755,000
Government-sponsored enterprise obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,987,000
Fair Value	4,545,000
Government-sponsored enterprise obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50,750,000
Fair Value	38,630,000
State and Municipal Obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,020,984,000	2,072,210,000
Fair Value	1,803,253,000	2,096,827,000
State and Municipal Obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	197,465,000
Fair Value	196,380,000
State and Municipal Obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	666,078,000
Fair Value	636,464,000
State and Municipal Obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	936,136,000
Fair Value	787,205,000
State and Municipal Obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	221,305,000
Fair Value	183,204,000
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,230,550,000	5,698,088,000
Fair Value	4,445,519,000	5,683,000,000
Non-Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,449,021,000	1,383,037,000
Fair Value	1,235,584,000	1,366,477,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,755,855,000	3,546,024,000
Fair Value	3,558,287,000	3,539,219,000
Total Mortgage And Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,435,426,000	10,627,149,000
Fair Value	9,239,390,000	10,588,696,000
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	579,193,000	633,524,000
Fair Value	510,367,000	$ 632,029,000
Other debt securities | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50,783,000
Fair Value	50,639,000
Other debt securities | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	272,029,000
Fair Value	249,688,000
Other debt securities | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	247,121,000
Fair Value	202,706,000
Other debt securities | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,260,000
Fair Value	$ 7,334,000