Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 15,425,954,000	$ 14,419,133,000
Fair Value	14,780,494,000	14,450,027,000
U.S. government and federal agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,115,041,000	1,035,477,000
Fair Value	1,129,961,000	1,080,720,000
U.S. government and federal agency obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	186,706,000
Fair Value	189,347,000
U.S. government and federal agency obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	746,460,000
Fair Value	746,770,000
U.S. government and federal agency obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	181,875,000
Fair Value	193,844,000
Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,765,000	50,773,000
Fair Value	51,390,000	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	5,000,000
Government-sponsored enterprise obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50,765,000
Fair Value	46,390,000
State and Municipal Obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,161,006,000	2,072,210,000
Fair Value	2,072,265,000	2,096,827,000
State and Municipal Obligations | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	181,848,000
Fair Value	182,560,000
State and Municipal Obligations | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	735,420,000
Fair Value	730,637,000
State and Municipal Obligations | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	917,122,000
Fair Value	860,827,000
State and Municipal Obligations | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	326,616,000
Fair Value	298,241,000
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,774,953,000	5,698,088,000
Fair Value	5,441,374,000	5,683,000,000
Non-Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,525,223,000	1,383,037,000
Fair Value	1,435,363,000	1,366,477,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,121,388,000	3,546,024,000
Fair Value	4,011,361,000	3,539,219,000
Total Mortgage And Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	11,421,564,000	10,627,149,000
Fair Value	10,888,098,000	10,588,696,000
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	672,578,000	633,524,000
Fair Value	638,780,000	$ 632,029,000
Other debt securities | Within 1 year
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	121,215,000
Fair Value	121,629,000
Other debt securities | After 1 but within 5 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	229,677,000
Fair Value	223,109,000
Other debt securities | After 5 but within 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	312,426,000
Fair Value	285,620,000
Other debt securities | After 10 years
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,260,000
Fair Value	$ 8,422,000