Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,783,369,000	$ 14,419,133,000
Fair Value	13,700,308,000	14,450,027,000
U.S. government and federal agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,125,536,000	1,035,477,000
Fair Value	1,109,128,000	1,080,720,000
U.S. government and federal agency obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	207,783,000
Fair Value	208,605,000
U.S. government and federal agency obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	731,507,000
Fair Value	718,407,000
U.S. government and federal agency obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	186,246,000
Fair Value	182,116,000
Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,758,000	50,773,000
Fair Value	47,108,000	51,755,000
Government-sponsored enterprise obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,000,000
Fair Value	4,922,000
Government-sponsored enterprise obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50,758,000
Fair Value	42,186,000
State and Municipal Obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,101,312,000	2,072,210,000
Fair Value	1,952,798,000	2,096,827,000
State and Municipal Obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	190,263,000
Fair Value	190,534,000
State and Municipal Obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	731,959,000
Fair Value	719,545,000
State and Municipal Obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	879,897,000
Fair Value	787,103,000
State and Municipal Obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	299,193,000
Fair Value	255,616,000
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,464,292,000	5,698,088,000
Fair Value	4,923,683,000	5,683,000,000
Non-Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,480,969,000	1,383,037,000
Fair Value	1,329,114,000	1,366,477,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,959,409,000	3,546,024,000
Fair Value	3,794,487,000	3,539,219,000
Total Mortgage And Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,904,670,000	10,627,149,000
Fair Value	10,047,284,000	10,588,696,000
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	596,093,000	633,524,000
Fair Value	543,990,000	$ 632,029,000
Other debt securities | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	64,757,000
Fair Value	64,704,000
Other debt securities | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	250,670,000
Fair Value	238,482,000
Other debt securities | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	271,406,000
Fair Value	232,905,000
Other debt securities | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,260,000
Fair Value	$ 7,899,000