Securities - Schedule of Unrealized Losses on Investment Securities (Detail) $ in Thousands	Jun. 30, 2024 USD ($) Security	Dec. 31, 2023 USD ($) Security
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 15,817	$ 20,407
Less than 12 months, Unrealized Losses	$ (209)	$ (136)
Less than 12 months, Number of Securities | Security	17	24
12 months or more, Fair Value	$ 2,013,652	$ 2,141,624
12 months or more, Unrealized Losses	$ (318,550)	$ (306,948)
12 months or more, Number of Securities | Security	665	654
Fair Value, Total	$ 2,029,469	$ 2,162,031
Unrealized Losses, Total	$ (318,759)	$ (307,084)
Number of Securities Total | Security	682	678
U.S. Government Sponsored Entities and Agencies [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value		$ 18
Less than 12 months, Unrealized Losses		$ (1)
Less than 12 months, Number of Securities | Security		1
12 months or more, Fair Value	$ 199,258	$ 208,348
12 months or more, Unrealized Losses	$ (32,654)	$ (30,309)
12 months or more, Number of Securities | Security	45	45
Fair Value, Total	$ 199,258	$ 208,366
Unrealized Losses, Total	$ (32,654)	$ (30,310)
Number of Securities Total | Security	45	46
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
12 months or more, Fair Value	$ 1,510,101	$ 1,625,144
12 months or more, Unrealized Losses	$ (277,066)	$ (267,874)
12 months or more, Number of Securities | Security	463	467
Fair Value, Total	$ 1,510,101	$ 1,625,144
Unrealized Losses, Total	$ (277,066)	$ (267,874)
Number of Securities Total | Security	463	467
Commercial Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value		$ 5,520
Less than 12 months, Unrealized Losses		$ (31)
Less than 12 months, Number of Securities | Security		1
12 months or more, Fair Value	$ 239,948	$ 251,765
12 months or more, Unrealized Losses	$ (5,000)	$ (5,893)
12 months or more, Number of Securities | Security	59	60
Fair Value, Total	$ 239,948	$ 257,285
Unrealized Losses, Total	$ (5,000)	$ (5,924)
Number of Securities Total | Security	59	61
Obligations of State and Political Subdivisions [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 11,336	$ 10,387
Less than 12 months, Unrealized Losses	$ (190)	$ (86)
Less than 12 months, Number of Securities | Security	13	19
12 months or more, Fair Value	$ 57,038	$ 49,002
12 months or more, Unrealized Losses	$ (3,669)	$ (2,775)
12 months or more, Number of Securities | Security	96	79
Fair Value, Total	$ 68,374	$ 59,389
Unrealized Losses, Total	$ (3,859)	$ (2,861)
Number of Securities Total | Security	109	98
Corporate Debt Securities [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 4,481	$ 4,482
Less than 12 months, Unrealized Losses	$ (19)	$ (18)
Less than 12 months, Number of Securities | Security	4	3
12 months or more, Fair Value	$ 7,307	$ 7,365
12 months or more, Unrealized Losses	$ (161)	$ (97)
12 months or more, Number of Securities | Security	2	3
Fair Value, Total	$ 11,788	$ 11,847
Unrealized Losses, Total	$ (180)	$ (115)
Number of Securities Total | Security	6	6