Securities - Gross Unrealized Losses and Fair Value of Investment Securities Held to Maturity (Detail) $ in Thousands	Mar. 31, 2022 USD ($) Security	Dec. 31, 2021 USD ($) Security
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	1,399	70
Less than 12 months, Fair Value	$ 4,029,571	$ 903,040
Less than 12 months,Unrealized Losses	$ (163,095)	$ (14,925)
12 months or more, Count | Security	41	28
12 months or more, Fair Value	$ 332,118	$ 217,579
12 months or more, Unrealized Losses	$ (46,059)	$ (26,460)
Total Count | Security	1,440	98
Total Fair Value	$ 4,361,689	$ 1,120,619
Total Unrealized Losses	$ (209,154)	$ (41,385)
Mortgage-backed [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	194	12
Less than 12 months, Fair Value	$ 2,404,509	$ 317,887
Less than 12 months,Unrealized Losses	$ (66,501)	$ (2,431)
Total Count | Security	194	12
Total Fair Value	$ 2,404,509	$ 317,887
Total Unrealized Losses	$ (66,501)	$ (2,431)
State and political subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	1,205	58
Less than 12 months, Fair Value	$ 1,625,062	$ 585,153
Less than 12 months,Unrealized Losses	$ (96,594)	$ (12,494)
12 months or more, Count | Security	41	28
12 months or more, Fair Value	$ 332,118	$ 217,579
12 months or more, Unrealized Losses	$ (46,059)	$ (26,460)
Total Count | Security	1,246	86
Total Fair Value	$ 1,957,180	$ 802,732
Total Unrealized Losses	$ (142,653)	$ (38,954)