Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value	$ 2,474,964	$ 77,449
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	21,474	179
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	89,767	3,156
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	2,237	19
Available-for-sale securities, continuous unrealized loss position, Fair Value	2,564,731	80,605
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	23,711	198
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	163,698	25,214
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	1,096	79
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	18,943	0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	122	0
Available-for-sale securities, continuous unrealized loss position, Fair Value	182,641	25,214
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1,218	79
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	2,263,010	36,017
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	19,742	96
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	54,392	3,156
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	1,544	19
Available-for-sale securities, continuous unrealized loss position, Fair Value	2,317,402	39,173
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	21,286	115
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	820	16,218
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	1	4
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
Available-for-sale securities, continuous unrealized loss position, Fair Value	820	16,218
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	1	$ 4
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	47,436
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss	635
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value	16,432
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss	571
Available-for-sale securities, continuous unrealized loss position, Fair Value	63,868
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss	$ 1,206