Securities - Gross Unrealized Losses and Fair Value of Investment Securities Available for Sale (Detail) $ in Thousands	Jun. 30, 2024 USD ($) Security	Dec. 31, 2023 USD ($) Security
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	445	411
Less than 12 months, Fair Value	$ 1,650,633	$ 734,181
Less than 12 months, Unrealized Losses	$ (17,945)	$ (9,949)
12 months or more, Count | Security	2,803	2,706
12 months or more, Fair Value	$ 4,867,782	$ 5,840,885
12 months or more, Unrealized Losses	$ (663,358)	$ (618,782)
Total Count | Security	3,248	3,117
Total Fair Value	$ 6,518,415	$ 6,575,066
Total Unrealized Losses	$ (681,303)	$ (628,731)
U.S. Treasury [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	60	8
Less than 12 months, Fair Value	$ 414,665	$ 509,946
Less than 12 months, Unrealized Losses	$ (2,430)	$ (267)
12 months or more, Count | Security	13	63
12 months or more, Fair Value	$ 172,775	$ 745,573
12 months or more, Unrealized Losses	$ (4,395)	$ (9,934)
Total Count | Security	73	71
Total Fair Value	$ 587,440	$ 1,255,519
Total Unrealized Losses	$ (6,825)	$ (10,201)
U.S. Agencies [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	13
Less than 12 months, Fair Value	$ 571,388
Less than 12 months, Unrealized Losses	$ (728)
12 months or more, Count | Security	7	16
12 months or more, Fair Value	$ 87,698	$ 116,324
12 months or more, Unrealized Losses	$ (1,923)	$ (2,937)
Total Count | Security	20	16
Total Fair Value	$ 659,086	$ 116,324
Total Unrealized Losses	$ (2,651)	$ (2,937)
Mortgage-backed [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	54	14
Less than 12 months, Fair Value	$ 360,634	$ 19,154
Less than 12 months, Unrealized Losses	$ (3,343)	$ (476)
12 months or more, Count | Security	848	852
12 months or more, Fair Value	$ 3,262,160	$ 3,526,296
12 months or more, Unrealized Losses	$ (542,134)	$ (508,264)
Total Count | Security	902	866
Total Fair Value	$ 3,622,794	$ 3,545,450
Total Unrealized Losses	$ (545,477)	$ (508,740)
State and political subdivisions [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	306	388
Less than 12 months, Fair Value	$ 214,127	$ 200,835
Less than 12 months, Unrealized Losses	$ (11,309)	$ (9,202)
12 months or more, Count | Security	1,677	1,476
12 months or more, Fair Value	$ 958,321	$ 890,545
12 months or more, Unrealized Losses	$ (89,079)	$ (65,785)
Total Count | Security	1,983	1,864
Total Fair Value	$ 1,172,448	$ 1,091,380
Total Unrealized Losses	$ (100,388)	$ (74,987)
Corporates [Member]
Gain (Loss) on Investments [Line Items]
12 months or more, Count | Security	249	267
12 months or more, Fair Value	$ 320,355	$ 351,275
12 months or more, Unrealized Losses	$ (25,675)	$ (30,794)
Total Count | Security	249	267
Total Fair Value	$ 320,355	$ 351,275
Total Unrealized Losses	$ (25,675)	$ (30,794)
Collateralized loan obligations [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	12	1
Less than 12 months, Fair Value	$ 89,819	$ 4,246
Less than 12 months, Unrealized Losses	$ (135)	$ (4)
12 months or more, Count | Security	9	32
12 months or more, Fair Value	$ 66,473	$ 210,872
12 months or more, Unrealized Losses	$ (152)	$ (1,068)
Total Count | Security	21	33
Total Fair Value	$ 156,292	$ 215,118
Total Unrealized Losses	$ (287)	$ (1,072)