Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 5,136,450	$ 2,474,964	$ 916,767
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	472,656	21,474	7,279
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	327,839	89,767	2,478
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	43,356	2,237	6
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	5,464,289	2,564,731	919,245
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	516,012	23,711	7,285
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	466,438
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	14,752
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	466,438
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	14,752
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	1,623,146	163,698	170,483
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	178,446	1,096	992
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	24,038	18,943
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	3,919	122
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,647,184	182,641	170,483
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	182,365	1,218	992
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	2,631,511	2,263,010	712,100
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	266,352	19,742	5,706
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	277,404	54,392	2,478
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	34,797	1,544	6
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,908,915	2,317,402	714,578
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	301,149	21,286	5,712
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	341,997	820	866
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	8,819	1
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	341,997	820	866
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	8,819	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	73,358	47,436	33,318
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss, Total	4,287	635	581
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	26,397	16,432
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	4,640	571
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	99,755	63,868	33,318
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	$ 8,927	$ 1,206	$ 581