Securities - Summary of Debt Securities with Unrealized Losses, Segregated by Duration of Unrealized Loss (Detail) $ in Thousands	Sep. 30, 2023 USD ($) Investments	Dec. 31, 2022 USD ($) Investments
Debt Securities, Available-for-Sale [Abstract]
Number of investments \| Investments	170	179
Available-for-sale Securities, Less than 12 Months, Fair Value	$ 97,531	$ 818,115
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	2,770	29,153
Available-for-sale Securities, 12 Months or Longer, Fair Value	1,408,140	698,341
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	98,447	64,771
Available-for-sale Securities, Fair Value, Total	1,505,671	1,516,456
Available-for-sale Securities, Unrealized Losses, Total	$ 101,217	$ 93,924
U.S. Treasuries [Member]
Debt Securities, Available-for-Sale [Abstract]
Number of investments \| Investments	71	74
Available-for-sale Securities, Less than 12 Months, Fair Value	$ 93,372	$ 787,925
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	2,708	27,078
Available-for-sale Securities, 12 Months or Longer, Fair Value	1,374,832	689,939
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	94,022	63,621
Available-for-sale Securities, Fair Value, Total	1,468,204	1,477,864
Available-for-sale Securities, Unrealized Losses, Total	$ 96,730	$ 90,699
U.S. Federal Agencies [Member]
Debt Securities, Available-for-Sale [Abstract]
Number of investments \| Investments	3	1
Available-for-sale Securities, Less than 12 Months, Fair Value	$ 1,260
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	3
Available-for-sale Securities, 12 Months or Longer, Fair Value		$ 349
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses		1
Available-for-sale Securities, Fair Value, Total	1,260	349
Available-for-sale Securities, Unrealized Losses, Total	$ 3	$ 1
Mortgage Backed Securities [Member]
Debt Securities, Available-for-Sale [Abstract]
Number of investments \| Investments	83	92
Available-for-sale Securities, Less than 12 Months, Fair Value	$ 1,242	$ 10,001
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	38	1,239
Available-for-sale Securities, 12 Months or Longer, Fair Value	12,887	5,055
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	2,434	645
Available-for-sale Securities, Fair Value, Total	14,129	15,056
Available-for-sale Securities, Unrealized Losses, Total	$ 2,472	$ 1,884
States and Political Subdivisions [Member]
Debt Securities, Available-for-Sale [Abstract]
Number of investments \| Investments	9	8
Available-for-sale Securities, Less than 12 Months, Fair Value	$ 1,657	$ 2,308
Available-for-sale Securities, Less than 12 Months, Unrealized Losses	21	184
Available-for-sale Securities, 12 Months or Longer, Fair Value	1,292	464
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	168	37
Available-for-sale Securities, Fair Value, Total	2,949	2,772
Available-for-sale Securities, Unrealized Losses, Total	$ 189	$ 221
Asset backed Securities [Member]
Debt Securities, Available-for-Sale [Abstract]
Number of investments \| Investments	1	1
Available-for-sale Securities, Less than 12 Months, Fair Value		$ 13,010
Available-for-sale Securities, Less than 12 Months, Unrealized Losses		361
Available-for-sale Securities, 12 Months or Longer, Fair Value	$ 12,411
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	378
Available-for-sale Securities, Fair Value, Total	12,411	13,010
Available-for-sale Securities, Unrealized Losses, Total	$ 378	$ 361
Other Securities [Member]
Debt Securities, Available-for-Sale [Abstract]
Number of investments \| Investments	3	3
Available-for-sale Securities, Less than 12 Months, Fair Value		$ 4,871
Available-for-sale Securities, Less than 12 Months, Unrealized Losses		291
Available-for-sale Securities, 12 Months or Longer, Fair Value	$ 6,718	2,534
Available-for-sale Securities, 12 Months or Longer, Unrealized Losses	1,445	467
Available-for-sale Securities, Fair Value, Total	6,718	7,405
Available-for-sale Securities, Unrealized Losses, Total	$ 1,445	$ 758

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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