Securities - Gross Unrealized Losses and Fair Value of Investment Securities Available for Sale (Detail) $ in Thousands	Jun. 30, 2023 USD ($) Security	Dec. 31, 2022 USD ($) Security
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	1,130	2,646
Less than 12 months, Fair Value	$ 995,481	$ 3,654,393
Less than 12 months, Unrealized Losses	$ (35,067)	$ (198,376)
12 months or more, Count | Security	2,130	674
12 months or more, Fair Value	$ 5,437,976	$ 3,098,117
12 months or more, Unrealized Losses	$ (732,406)	$ (575,017)
Total Count | Security	3,260	3,320
Total Fair Value	$ 6,433,457	$ 6,752,510
Total Unrealized Losses	$ (767,473)	$ (773,393)
U.S. Treasury [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	8	61
Less than 12 months, Fair Value	$ 56,846	$ 688,208
Less than 12 months, Unrealized Losses	$ (673)	$ (22,731)
12 months or more, Count | Security	61	4
12 months or more, Fair Value	$ 730,978	$ 55,314
12 months or more, Unrealized Losses	$ (22,273)	$ (4,415)
Total Count | Security	69	65
Total Fair Value	$ 787,824	$ 743,522
Total Unrealized Losses	$ (22,946)	$ (27,146)
U.S. Agencies [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security		27
Less than 12 months, Fair Value		$ 140,877
Less than 12 months, Unrealized Losses		$ (4,734)
12 months or more, Count | Security	29	2
12 months or more, Fair Value	$ 172,301	$ 30,419
12 months or more, Unrealized Losses	$ (5,811)	$ (2,231)
Total Count | Security	29	29
Total Fair Value	$ 172,301	$ 171,296
Total Unrealized Losses	$ (5,811)	$ (6,965)
Mortgage-backed [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	157	687
Less than 12 months, Fair Value	$ 445,406	$ 1,415,169
Less than 12 months, Unrealized Losses	$ (24,090)	$ (102,881)
12 months or more, Count | Security	719	205
12 months or more, Fair Value	$ 3,257,924	$ 2,557,035
12 months or more, Unrealized Losses	$ (570,897)	$ (489,994)
Total Count | Security	876	892
Total Fair Value	$ 3,703,330	$ 3,972,204
Total Unrealized Losses	$ (594,987)	$ (592,875)
State and political subdivisions [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	953	1,744
Less than 12 months, Fair Value	$ 449,733	$ 936,865
Less than 12 months, Unrealized Losses	$ (9,411)	$ (51,427)
12 months or more, Count | Security	1,022	273
12 months or more, Fair Value	$ 689,601	$ 233,679
12 months or more, Unrealized Losses	$ (87,549)	$ (53,372)
Total Count | Security	1,975	2,017
Total Fair Value	$ 1,139,334	$ 1,170,544
Total Unrealized Losses	$ (96,960)	$ (104,799)
Corporates [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	7	86
Less than 12 months, Fair Value	$ 14,500	$ 146,615
Less than 12 months, Unrealized Losses	$ (758)	$ (8,783)
12 months or more, Count | Security	262	189
12 months or more, Fair Value	$ 328,156	$ 216,885
12 months or more, Unrealized Losses	$ (41,441)	$ (24,776)
Total Count | Security	269	275
Total Fair Value	$ 342,656	$ 363,500
Total Unrealized Losses	$ (42,199)	$ (33,559)
Collateralized loan obligations [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	5	41
Less than 12 months, Fair Value	$ 28,996	$ 326,659
Less than 12 months, Unrealized Losses	$ (135)	$ (7,820)
12 months or more, Count | Security	37	1
12 months or more, Fair Value	$ 259,016	$ 4,785
12 months or more, Unrealized Losses	$ (4,435)	$ (229)
Total Count | Security	42	42
Total Fair Value	$ 288,012	$ 331,444
Total Unrealized Losses	$ (4,570)	$ (8,049)