Securities - Schedule of Unrealized Losses on Investment Securities (Detail) $ in Thousands	Sep. 30, 2023 USD ($) Security	Dec. 31, 2022 USD ($) Security
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 34,749	$ 887,036
Less than 12 months, Unrealized Losses	$ (1,035)	$ (54,828)
Less than 12 months, Number of Securities | Security	37	498
12 months or more, Fair Value	$ 2,154,652	$ 1,619,473
12 months or more, Unrealized Losses	$ (391,913)	$ (291,079)
12 months or more, Number of Securities | Security	668	264
Fair Value, Total	$ 2,189,401	$ 2,506,509
Unrealized Losses, Total	$ (392,948)	$ (345,907)
Number of Securities Total | Security	705	762
U.S. Government Sponsored Entities and Agencies [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value		$ 107,011
Less than 12 months, Unrealized Losses		$ (8,435)
Less than 12 months, Number of Securities | Security		35
12 months or more, Fair Value	$ 201,494	$ 118,779
12 months or more, Unrealized Losses	$ (40,592)	$ (25,015)
12 months or more, Number of Securities | Security	45	13
Fair Value, Total	$ 201,494	$ 225,790
Unrealized Losses, Total	$ (40,592)	$ (33,450)
Number of Securities Total | Security	45	48
Residential 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		$ 514,789
Less than 12 months, Unrealized Losses		$ (39,246)
Less than 12 months, Number of Securities | Security		294
12 months or more, Fair Value	$ 1,613,653	$ 1,328,906
12 months or more, Unrealized Losses	$ (337,659)	$ (258,741)
12 months or more, Number of Securities | Security	472	202
Fair Value, Total	$ 1,613,653	$ 1,843,695
Unrealized Losses, Total	$ (337,659)	$ (297,987)
Number of Securities Total | Security	472	496
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	$ 5,574	$ 190,189
Less than 12 months, Unrealized Losses	$ (41)	$ (5,106)
Less than 12 months, Number of Securities | Security	1	38
12 months or more, Fair Value	$ 283,445	$ 159,543
12 months or more, Unrealized Losses	$ (8,201)	$ (4,974)
12 months or more, Number of Securities | Security	64	36
Fair Value, Total	$ 289,019	$ 349,732
Unrealized Losses, Total	$ (8,242)	$ (10,080)
Number of Securities Total | Security	65	74
Obligations of State and Political Subdivisions [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 24,713	$ 67,822
Less than 12 months, Unrealized Losses	$ (956)	$ (1,815)
Less than 12 months, Number of Securities | Security	33	128
12 months or more, Fair Value	$ 48,863	$ 7,812
12 months or more, Unrealized Losses	$ (5,199)	$ (2,282)
12 months or more, Number of Securities | Security	84	10
Fair Value, Total	$ 73,576	$ 75,634
Unrealized Losses, Total	$ (6,155)	$ (4,097)
Number of Securities Total | Security	117	138
Corporate Debt Securities [Member]
Net Unrealized Gains And Losses On Investments [Line Items]
Less than 12 months, Fair Value	$ 4,462	$ 7,225
Less than 12 months, Unrealized Losses	$ (38)	$ (226)
Less than 12 months, Number of Securities | Security	3	3
12 months or more, Fair Value	$ 7,197	$ 4,433
12 months or more, Unrealized Losses	$ (262)	$ (67)
12 months or more, Number of Securities | Security	3	3
Fair Value, Total	$ 11,659	$ 11,658
Unrealized Losses, Total	$ (300)	$ (293)
Number of Securities Total | Security	6	6