Securities - Gross Unrealized Losses and Fair Value of Investment Securities Held to Maturity (Detail) $ in Thousands	Sep. 30, 2022 USD ($) Security	Dec. 31, 2021 USD ($) Security
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	1,721	70
Less than 12 months, Fair Value	$ 4,520,742	$ 903,040
Less than 12 months,Unrealized Losses	$ (698,535)	$ (14,925)
12 months or more, Count | Security	52	28
12 months or more, Fair Value	$ 414,718	$ 217,579
12 months or more, Unrealized Losses	$ (59,650)	$ (26,460)
Total Count | Security	1,773	98
Total Fair Value	$ 4,935,460	$ 1,120,619
Total Unrealized Losses	$ (758,185)	$ (41,385)
U.S. Agencies [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	11
Less than 12 months, Fair Value	$ 118,923
Less than 12 months,Unrealized Losses	$ (4,139)
Total Count | Security	11
Total Fair Value	$ 118,923
Total Unrealized Losses	$ (4,139)
Mortgage-backed [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	261	12
Less than 12 months, Fair Value	$ 2,636,255	$ 317,887
Less than 12 months,Unrealized Losses	$ (380,177)	$ (2,431)
Total Count | Security	261	12
Total Fair Value	$ 2,636,255	$ 317,887
Total Unrealized Losses	$ (380,177)	$ (2,431)
State and political subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	1,449	58
Less than 12 months, Fair Value	$ 1,765,564	$ 585,153
Less than 12 months,Unrealized Losses	$ (314,219)	$ (12,494)
12 months or more, Count | Security	52	28
12 months or more, Fair Value	$ 414,718	$ 217,579
12 months or more, Unrealized Losses	$ (59,650)	$ (26,460)
Total Count | Security	1,501	86
Total Fair Value	$ 2,180,282	$ 802,732
Total Unrealized Losses	$ (373,869)	$ (38,954)