Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 1,909,674	$ 2,474,964
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	118,033	21,474
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	3,378,251	89,767
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	561,193	2,237
Available-for-sale securities, continuous unrealized loss position, Fair Value	5,287,925	2,564,731
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	679,226	23,711
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	307,012
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	11,650
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	173,105
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	14,087
Available-for-sale securities, continuous unrealized loss position, Fair Value	480,117
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	25,737
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	770,469	163,698
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	55,943	1,096
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	946,571	18,943
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	150,856	122
Available-for-sale securities, continuous unrealized loss position, Fair Value	1,717,040	182,641
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	206,799	1,218
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	470,970	2,263,010
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	37,065	19,742
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	2,143,869	54,392
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	380,497	1,544
Available-for-sale securities, continuous unrealized loss position, Fair Value	2,614,839	2,317,402
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	417,562	21,286
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	319,303	820
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	11,677	1
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	54,862	0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	6,369	0
Available-for-sale securities, continuous unrealized loss position, Fair Value	374,165	820
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	18,046	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	41,920	47,436
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	1,698	635
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	59,844	16,432
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	9,384	571
Available-for-sale securities, continuous unrealized loss position, Fair Value	101,764	63,868
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	$ 11,082	$ 1,206