Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 16,963	$ 1,909,674
Unrealized Gain (Loss) on Derivatives	42	118,033
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	4,655,649	3,378,251
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	511,822	561,193
Available-for-sale securities, continuous unrealized loss position, Fair Value	4,672,612	5,287,925
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	511,864	679,226
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	3,477	307,012
Unrealized Gain (Loss) on Derivatives	7	11,650
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	477,306	173,105
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	14,738	14,087
Available-for-sale securities, continuous unrealized loss position, Fair Value	480,783	480,117
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	14,745	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	11,855	770,469
Unrealized Gain (Loss) on Derivatives	34	55,943
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	1,427,975	946,571
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	125,148	150,856
Available-for-sale securities, continuous unrealized loss position, Fair Value	1,439,830	1,717,040
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	125,182	206,799
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	1,631	470,970
Unrealized Gain (Loss) on Derivatives	1	37,065
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	2,361,089	2,143,869
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	352,882	380,497
Available-for-sale securities, continuous unrealized loss position, Fair Value	2,362,720	2,614,839
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	352,883	417,562
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	0	319,303
Unrealized Gain (Loss) on Derivatives	0	11,677
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	284,324	54,862
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	11,339	6,369
Available-for-sale securities, continuous unrealized loss position, Fair Value	284,324	374,165
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	11,339	18,046
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	0	41,920
Unrealized Gain (Loss) on Derivatives	0	1,698
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	104,955	59,844
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	7,715	9,384
Available-for-sale securities, continuous unrealized loss position, Fair Value	104,955	101,764
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	$ 7,715	$ 11,082