Securities - Schedule of Unrealized Losses on Investment Securities (Detail) $ in Thousands	Mar. 31, 2024 USD ($) Security	Dec. 31, 2023 USD ($) Security
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 15,289	$ 20,407
Less than 12 months, Unrealized Losses	$ (83)	$ (136)
Less than 12 months, Number of Securities | Security	14	24
12 months or more, Fair Value	$ 2,076,993	$ 2,141,624
12 months or more, Unrealized Losses	$ (318,498)	$ (306,948)
12 months or more, Number of Securities | Security	669	654
Fair Value, Total	$ 2,092,282	$ 2,162,031
Unrealized Losses, Total	$ (318,581)	$ (307,084)
Number of Securities Total | Security	683	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	$ 201,709	$ 208,348
12 months or more, Unrealized Losses	$ (32,998)	$ (30,309)
12 months or more, Number of Securities | Security	45	45
Fair Value, Total	$ 201,709	$ 208,366
Unrealized Losses, Total	$ (32,998)	$ (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	$ 1,568,530	$ 1,625,144
12 months or more, Unrealized Losses	$ (276,658)	$ (267,874)
12 months or more, Number of Securities | Security	466	467
Fair Value, Total	$ 1,568,530	$ 1,625,144
Unrealized Losses, Total	$ (276,658)	$ (267,874)
Number of Securities Total | Security	466	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	$ 243,531	$ 251,765
12 months or more, Unrealized Losses	$ (5,386)	$ (5,893)
12 months or more, Number of Securities | Security	60	60
Fair Value, Total	$ 243,531	$ 257,285
Unrealized Losses, Total	$ (5,386)	$ (5,924)
Number of Securities Total | Security	60	61
Obligations of State and Political Subdivisions [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 8,811	$ 10,387
Less than 12 months, Unrealized Losses	$ (61)	$ (86)
Less than 12 months, Number of Securities | Security	10	19
12 months or more, Fair Value	$ 58,392	$ 49,002
12 months or more, Unrealized Losses	$ (3,323)	$ (2,775)
12 months or more, Number of Securities | Security	97	79
Fair Value, Total	$ 67,203	$ 59,389
Unrealized Losses, Total	$ (3,384)	$ (2,861)
Number of Securities Total | Security	107	98
Corporate Debt Securities [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 6,478	$ 4,482
Less than 12 months, Unrealized Losses	$ (22)	$ (18)
Less than 12 months, Number of Securities | Security	4	3
12 months or more, Fair Value	$ 4,831	$ 7,365
12 months or more, Unrealized Losses	$ (133)	$ (97)
12 months or more, Number of Securities | Security	1	3
Fair Value, Total	$ 11,309	$ 11,847
Unrealized Losses, Total	$ (155)	$ (115)
Number of Securities Total | Security	5	6