Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 4,258,183	$ 2,474,964	$ 1,812,030
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	537,139	21,474	13,987
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	1,367,993	89,767	20,762
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	264,420	2,237	471
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	5,626,176	2,564,731	1,832,792
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	801,559	23,711	14,458
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	476,696
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	27,283
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	476,696
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	27,283
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	1,828,105	163,698	570,916
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	254,212	1,096	6,036
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	139,732	18,943	18,711
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	31,095	122	467
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,967,837	182,641	589,627
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	285,307	1,218	6,503
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	1,507,121	2,263,010	1,208,129
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	231,915	19,742	7,166
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	1,187,815	54,392	2,051
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	225,082	1,544	4
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,694,936	2,317,402	1,210,180
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	456,997	21,286	7,170
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	386,479	820
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	19,185	1
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	0	0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	386,479	820
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	19,185	1
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	59,782	47,436	32,985
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	4,544	635	785
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	40,446	16,432	0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	8,243	571	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	100,228	63,868	32,985
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	$ 12,787	$ 1,206	$ 785